Chapter 12: Canadian Tuberculosis Standards 7th Edition: 2014 – Contact follow-up and outbreak management in Tuberculosis control

There is often pressure on a public health department or physician to initiate widespread contact investigation - e.g. to an entire school - from the outset. If this is done, however, it is often impossible to interpret the results of a positive TST result (or interferon gamma release assay [IGRA]) in individual patients. Contacts may then be mistakenly identified as recently infected and the investigation expanded yet further. This can also lead to widespread concern about the risk of transmission to community contacts. If expansion of the investigation beyond high- and medium-priority groups is considered, the decision should be based on evaluation of any evidence of transmission in the initial investigation, the probability of finding infected individuals among less exposed contacts and the likelihood that these casual contacts will follow up on screening and LTBI treatment recommendations. Contacts with less exposure have a positive TST prevalence rate that is usually four to eight times less than that among household contacts^{Footnote 4 Footnote 8 Footnote 33 Footnote 34}. Also, contact participation rates in TB screening, follow-up and LTBI treatment tend to be lower in less close contacts, contacts of less infectious cases and in adults compared with children^{Footnote 35}.

Additional Approaches to Contact Tracing

DNA genotype fingerprinting:

DNA fingerprinting is available to all Canadian TB control programs, on request or routinely, through the public health laboratories. It can be a useful adjunct to epidemiologic investigations to confirm or disprove suspected linkages between cases and to evaluate potential specimen mix-upsFootnote 36 Footnote 37. It can be particularly helpful in populations in which contact follow-up is challenging and resource intensive, such as the homeless; routine use of fingerprinting for homeless cases may identify linkages not otherwise suspected and guide expanded contact investigationFootnote 38 Footnote 39. Rapid fingerprinting techniques (spoligotyping, MIRU [Mycobacterium Interspersed Repetitive Units]) are helpful to quickly identify or rule out potential new cases in evolving clusters or outbreaks. Fingerprinting can also be very useful, and reassuring, in the evaluation of potential clusters if the results do not show matching outside known household secondary cases.

Location-based contact investigation and social network analysis:

All cases should routinely be asked about the locations where they spend time. Particularly when infectious cases are unable or unwilling to name specific contacts, or when cases are occurring without identifiable exposure risks or sources, identifying locations where the case spent time may be more productive than traditional name-based approaches^{Footnote 40}.Investigations have identified transmission occurring at bars, crack use sites, etc.,^{Footnote 41-43}  which can then be targeted for broad location-based screening clinics and TB education/outreach. Epidemiologic links among cases can be enhanced when questions about common locations are included in case interviews.

Social networks analysis examines the social relationships between cases and contacts to identify settings and behaviours that characterize transmission events. Social network analysis has been extensively studied in sexually transmitted infections and more recently in the study of TB outbreaks^{Footnote 40 Footnote 43-45}. Formal social network analysis, using special computer software, may be particularly helpful in outbreaks (refer to Pajek-Program for Large Network Analysis).

Site-base screening and congregate settings:

In some settings, it is far more practical and feasible to carry out contact investigation for an entire group (such as a class at school or coworkers in a work setting) than attempt to identify the specific individuals who were most exposed. Practical factors, such as the ability to reliably measure the degree of exposure of different individuals in the setting, the administrative ability to provide efficient testing and TB education, and the ramifications of extending the investigation to a larger group later if it becomes necessary, should be taken into account in deciding on the extent and number of people to be tested. Similarly, in certain settings (e.g. shelters for the homeless) in which contacts may be difficult to identify or to find, it may be helpful to do wider testing from the outset.

School, workplace and other congregate setting investigations are usually best carried out on site. This leads to higher participation rates among contacts, better communication and less anxiety; it is usually the most effective and efficient way of carrying out the investigation and obtaining the necessary information. However, for this type of investigation it is important to be very organized. The following approach is recommended:

• Identify a single individual at the setting who will be responsible for organizational aspects of the contact investigation and act as liaison, usually a school principal, workplace manager or occupational health manager.
• Protect the confidentiality of the index case (Note investigations should be carried out in compliance with relevant legal/legislative requirements, and that provincial/territorial legislation may permit disclosure in specific circumstances). This may not be easy; there may be considerable pressure for details, and in many situations others may be able to guess the identity of the case. Particularly if the identity of the case is widely known or suspected, enlist the help of setting personnel (e.g. the principal or manager) to plan for successful reintegration of the TB case once noninfectious.
• Visit the site beforehand to get a sense of the environment and organize the screening arrangements; get input from the setting's liaison person to ensure that screening is carried out at a time and in a way that offers the best opportunity for contacts to come to the screening.
• Check that adequate staffing will be available for the screening.
• Include key players at the site, such as occupational health services, human resources or other administrative staff, and union health and safety representatives in planning and communication; they may benefit from information about TB ahead of a general information session as others will likely look to them for advice.
• Prepare a communication plan; identify one individual who will be responsible for media and communications to the general public if necessary; alert public health communications staff.
• Offer general information/education sessions about TB and the contact follow-up for all parents/employees/residents before the screening sessions; if the number of contacts is relatively small, a separate session specifically for them may be helpful.
• Identify the referral plan for contacts who are TST positive or symptomatic; treat all contacts referred for medical evaluation consistently, ideally by a limited number of health care providers working in coordination with public health. It can be confusing and alarming for a group of contacts if the work-up and treatment advice are inconsistent from person to person.
• Ensure the results of the medical evaluation are provided promptly to the appropriate public health authority.

Contact investigations carried out in work or school settings may be associated with high levels of anxiety. Good organization, communication and transparency (to the extent possible while protecting case confidentiality) are critical aspects of all site-based or expanded contact investigations. Anxiety and misinformation can be minimized by limiting the delay between contacting the site and conducting testing, ensuring that key people at the setting get the same information at the same time, and by holding general education sessions about TB and the investigation plan. Communication from all personnel involved in the investigation should be clear, credible and consistent, especially with regard to the actual level of risk involved, interpretation of the TST and decisions regarding treatment of LTBI.

A standard approach to the evaluation of contacts for the presence of active disease and evidence of recent infection:

All identified contacts should be interviewed systematically regarding their exposure to the case, presence of symptoms, risk factors for progression to active TB if infected and history of treatment of TB or LTBI. If there are any concerns, rapid evaluation to exclude active TB should be carried out. Once active disease has been excluded, contacts should receive a TST unless there is a history of prior treatment of TB or a documented prior positive TST result. The TST should be carried out and interpreted regardless of BCG vaccination status. A TST of 5 mm or more is considered positive for contacts. Refer also to Chapter 4, Chapter 6 and Chapter 9, Pediatric Tuberculosis.

Note that TB assessment of contacts may involve TST or an IGRA (refer to Chapter 4, Diagnosis of Latent Tuberculosis Infection).

A two-step TST is not recommended in the setting of a contact investigation: Skin test conversion can occur as early as 3 weeks after exposure, and it will generally be impossible to differentiate between true TST conversion and a boosted reaction in the setting of a contact investigation (refer to Chapter 2 and Chapter 4). This is another reason why only those with significant exposure should be considered contacts.

Window treatment of LTBI for those most susceptible: Contacts who are at very high risk of progression to active disease if infected (children under 5 years; HIV positive or other immunosuppressed individuals) should receive window prophylaxis in the interval between a negative initial TST result and the definitive TST at least 8 weeks after the last day of exposure because of the high risk of progression to active TB if infected. Refer to Chapter 6 and Chapter 9 for additional information.

Evaluation of Contact Investigation:

The results of each contact investigation should be reviewed as they become available, to guide expansion and/or additional follow-up efforts. In addition, program-wide outcomes should be reviewed annually. Along with qualitative assessment of successes and challenges, they are important elements for program evaluation and future planning. Key indicators should include the following:

• initial list of contacts for each infectious TB case, completed within 7 calendar days;
• assessment of close contacts completed and LTBI treatment started, if indicated and not contraindicated or refused, within 28 calendar days;
• proportion of contacts with a diagnosis of LTBI who begin treatment;
• proportion of contacts beginning treatment for LTBI who complete treatment; and
• proportion of contacts completing LTBI treatment who show active TB disease within 2 years after completion.

Summary Points

Recommended Steps in Contact Investigation and Follow-Up

1. The treating physician and laboratory should report all new or suspected cases of TB within 48 hours to the appropriate public health authorities.
2. Each new active case should be interviewed by public health authorities to identify household and other close contacts promptly. TB programs should prioritize contacts by the infectiousness of the source case, the extent of the exposure and the risk of progression to active TB if infected.
3. Each contact should be interviewed regarding the circumstances and duration of exposure, presence of symptoms, previous history of tuberculosis, TB exposure and prior TST.
4. Public health authorities and the treating physician should collaborate to ensure that contacts with no previous history of TB or documented positive tests receive a TST and symptom assessment.
5. In the context of contact investigation, a positive TST result is 5 mm or greater on initial or repeat testing, or an increase of at least 6 mm from a previous TST of 5-9 mm. A history of BCG vaccination does not alter the interpretation of the skin test results for contacts. TST should be repeated at least 8 weeks after the last exposure for all high-priority contacts who had an initial negative test. Refer to Chapter 4, Diagnosis of Latent Tuberculosis Infection, for guidance.
6. A medical evaluation to rule out active TB should be performed for all contacts who have symptoms compatible with TB; a positive TST result, whether before exposure or at initial or repeat testing; and (regardless of the results of the initial TST) all children under age 5, as well as contacts who are HIV seropositive or severely immunocompromised, according to the recommendations in Chapter 3, Diagnosis of Active Tuberculosis and Drug Resistance, Chapter 9, Pediatric Tuberculosis, and Chapter 10, Tuberculosis and Human Immunodeficiency Virus. This should include chest radiography, plus sputum collection as indicated.
7. Once active TB has been ruled out, treatment of LTBI should be offered according to the recommendations in Chapter 6, Treatment of Latent Tuberculosis Infection, Chapter 9, Pediatric Tuberculosis, and Chapter 10, Tuberculosis and Human Immunodeficiency Virus.
8. Public health authorities should determine the need to extend the contact investigation on the basis of the contagiousness of the index case, the results of the investigation of high-priority contacts and the nature of the exposure of additional contacts.
9. Extended contact investigations should be carried out in a systematic and organized manner; public health/TB control should coordinate these investigations.

The results of the contact investigation should be evaluated by the TB management program.

Contact Investigations in Special Settings

Homeless and Underhoused People and Those with Drug Addictions

Contact tracing for cases who are homeless, heavy users of illicit drugs and other highly marginalized individuals is very challenging and resource intensive. It is easy to become frustrated and overwhelmed. These challenges can be made more manageable and successful by recognizing that such cases are not "business as usual," keeping priorities clearly in mind, training staff and allocating adequate resources.

Many homeless TB cases may suffer from alcoholism, drug addiction or mental illness, which complicates the management of their TB^{Footnote 46}.They may have poor access to health services and multiple medical comorbidities, resulting in delayed TB diagnosis, worsening of the disease, prolonged periods of infectiousness and thus large numbers of contacts who need to be assessed. High baseline prevalence rates of TST positivity also mean that a large number of contacts will require further assessment and possible treatment of LTBI ^{Footnote 47-51}.

Information that is easily collected from other individuals with TB can prove very difficult to gather from homeless individuals. They may not know the names of friends/associates or only a street name, or where to find them; recall may be severely limited by addiction or mental illness and sometimes by mistrust of authorities. Drug users may be very reluctant to implicate those they use drugs with for fear of legal prosecution. It may be most productive to try to identify any particularly close friends by name and otherwise to focus on setting-based follow-up. Cases may be highly mobile, with many locations exposed. Shelters may have bed logs, which can be used to identify room-mates; in large shared rooms, prioritize those who spent the most nights with the case and slept closest. Bear in mind that ventilation patterns, including fans, can affect transmission. Rooming houses (also known as single-room occupancy hotels) are often very cramped and poorly ventilated. Homeless shelters may be closed during the day; ask about meals, drop-in centres providing services for the homeless (day-use shelters), libraries, bars, parks, etc. Shelter staff or social service agency workers may be able to identify daily patterns, or friends, and family of the case. If there are gaps in the available history during the infectious period, it may also be worthwhile to check for recent hospitalizations or detainment in a correctional facility. It will be extremely helpful to involve staffs who are familiar with the local homeless sector in contact follow-up.

Homeless contacts are often difficult to locate, and have significant challenges following through on screening, medical evaluation, and preventive treatment for LTBIFootnote 52.Non-judgmental and supportive TB staff, and judicious use of incentives and enablers may help increase participation rates. Active participation and encouragement from trusted staff at the shelter or day-program (e.g. a drop-in centre or soup kitchen) during screening clinics is especially helpful. Persistence and flexibility are critical. Someone who is not co-operative one day may be willing to participate another time; interventions which can be carried out on-site or in a single session generally have more success than those involving extra visits or travel (e.g. sputum collection on site, portable chest x-ray , IGRA vs TST planting and reading)Footnote 53-55. The primary focus should generally be on early detection of secondary cases; LTBI should be assessed and treated only if individuals meet the medical and social criteria for treatment of LTBI.

Refer also to Chapter 15, Prevention and Control of Tuberculosis Transmission in Health Care and Other Settings, for additional discussion on the prevention of TB in homeless shelters.

Correctional Facilities

Residents of correctional facilities often have a higher prevalence of TB infection and disease; large outbreaks of TB have occurred in prisons in the United States, Russia and elsewhereFootnote 56-58. Older facilities in particular are often overcrowded and poorly ventilated, increasing the risk of spread. Some residents have comorbid medical conditions, such as HIV infection, that increase progression of TB infection to active disease; mental illness and mistrust of authorities can make clinical assessment difficult.

When an infectious case of TB is identified in a correctional facility, contacts can include fellow inmates and employees at the facility, transportation staff, visitors, courthouses, and family or community members exposed before the case was incarcerated. Multiple corrections facilities may be involved, as both provincial and federal inmates are often moved between sites, and both case and contacts may have had multiple incarcerations during the infectious period^{Footnote 45}.However, where inmates are given a TST on admission and/or annually, these results may be available as a baseline for contact follow-up. To assist in the identification of contacts, correctional facilities should track inmate transfers, releases and movement within a facility and within the system.

Levels of anxiety may be very high among corrections staff during a TB investigation and have sometimes resulted in facility closures or work stoppages. Ongoing relationships with local public health/TB control staff can help mitigate this. It is extremely helpful to include senior corrections staff, particularly chiefs/directors of health care, and union health and safety representatives early in planning and communication; if multiple facilities are involved, provincial/territorial or senior federal corrections officials should be included. If suspect cases are identified during contact follow-up, they should be removed from the general ranges/shared cells pending diagnostic confirmation. Suspect and confirmed infectious cases should be kept in airborne isolation rooms if available within correctional facilities or transferred to hospital.

Correctional Service Canada has developed guidelines for TB prevention and control in institutions that house inmates sentenced to 2 years or longer. Contact publichealth@csc-scc.gc.ca to obtain a copy.

Health Care Institutions

Hospital TB contact follow-up benefits from close coordination and collaboration between public health/TB control staff and hospital infection control/occupational health staff. While almost every type of health care institution has been implicated in nosocomial transmission, there is very little by way of published hospital contact follow-up studies to guide thoughtful contact follow-up^{Footnote 59-61}. Unless the contact investigation is conducted in an organized, systematic fashion, with the basic principles of transmission in mind, it may result in hundreds of "contacts" with limited or unknowable exposure and often dismal participation and follow-up completion rates. It is often very useful to measure air exchange rates in specific hospital exposure locations, in order to help prioritize contact follow-up. It is also important to confirm whether there were any unprotected aerosolizing procedures, such as intubation, carried out on the infectious case (i.e. when staff did not use N95 masks). Some types of patients are extremely vulnerable (e.g. transplant patients) and even short exposures may be relevant (refer to Chapter 6). Visitors to the case and to room-mates may have significant exposure. Hospital infection control and occupational health departments often take advantage of TB exposures to get staff TST documentation up to date, but within this larger group of staff being tested it is important to distinguish those who have the most actual exposure to the infectious case - particularly if there are conversions detected. Pooling the results of contact follow-up within and outside of the hospital can help to focus the investigation and determine the need, if any, for expansion. Notification of contacts may come from the hospital and/or public health authority, and testing can be done by the hospital, public health authority or personal physicians, but the plan should be agreed on by all parties to avoid confusion and gaps.

Individuals who are immunosuppressed are at much higher risk of TB disease after infection with TB; thus, TB exposures in specialty services or clinics may pose an especially high risk. For example, among dialysis patients in British Columbia, the annual rate of TB was 25 times higher than among age-matched population controlsFootnote 62.Nosocomial transmission of TB to people with HIV is well documented in both inpatient and outpatient settingsFootnote 63 Footnote 64. Refer to Chapter 4, Diagnosis of Latent Tuberculosis Infection, Chapter 6, Treatment of Latent Tuberculosis Infection, and Chapter 10, Tuberculosis and Human Immunodeficiency Virus, for additional information on assessment and management of these contacts. Also, refer to Chapter 15, Prevention and Control of Tuberculosis Transmission in Health Care and Other Settings.

Long-Term Care

Many of the same issues for hospitals apply to TB exposures in long-term care facilities. For residents who are contacts of an infectious case of TB, the most critical follow-up is assessment for active disease through careful symptom evaluation, chest radiography and sputum testing. Diagnosis of active TB in the elderly can be difficult, and expert clinical consultation may be necessary. Gastric washings may be easier to obtain than spontaneous or induced sputum in demented or very elderly residents. TST is not recommended as a primary contact assessment tool for residents over 65 years^{Footnote 65}.Interpretation of TST results in the elderly is often complicated by both immune suppression and the potential for boosting related to remote TB exposure or BCG^{Footnote 66-69}. As well, for many elderly contacts the risks of LTBI treatment outweigh the potential benefits. However, contacts among staff and visitors ≤65 years old should receive a TST. In the absence of secondary cases, their results are likely to be a more reliable indicator of transmission in the facility.

Remote Communities

Contact investigation in a remote community may be especially challenging. Access to diagnostic tests, staffing, TB expertise and resources may be difficult. In remote First Nations or Inuit communities there may also be significant language and cultural barriers to successful contact tracing. Nowhere are organization, education, communication and a collaborative, nonjudgmental approach more important. The provincial/territorial TB program, the local public health/TB control program, Health Canada's First Nations and Inuit Health Branch if it is involved in the delivery or funding of health services in the community, local health care providers and the community should work closely together to identify secondary cases and contacts quickly, and then to see that they are properly managed over the duration of medical investigation and treatment. A mobile or portable radiography unit may need to be brought to the community; liberal use of sputum screening may also be useful in coordination with the public health laboratory. Otherwise, a special effort should be made to facilitate the timely transport of people with suspected TB to a larger medical centre for investigation. Directly observed preventive therapy is a treatment option for newly infected contacts in First Nations and Inuit communitiesFootnote 70.Also, refer to Chapter 14, Tuberculosis Prevention and Care in First Nations, Inuit and Métis Peoples.

Contacts During Air Travel and Other Public Transport

The World Health Organization (WHO) publishes guidelines^{Footnote 71} outlining the procedures for notifying certain contacts of people with infectious TB who have travelled on an international flight with a total duration of ≥8 hours within the previous 3 months. The 8 hour duration is based on epidemiologic studies reviewed in the WHO guidelines. In Canada, reports of people with TB who report a history of air travel while infectious should be made to the Public Health Agency of Canada (PHAC) through the provincial/territorial TB program (even if the flight occurred more than 3 months ago, as passenger records are usually still available). The reporting form and detailed guidelines can be found at Public Health Agency of Canada, Reporting Forms website. The report to PHAC should be made as soon as possible (even if culture and antibiotic sensitivity results are still pending), as this speeds up the process of risk assessment and securing the necessary passenger information from the airline. However, a systematic review of 12 studies suggests that the value of actively screening airplane passengers is limited^{Footnote 72}.

The few published reports of contact tracing after exposure to TB on buses and trains indicate that transmission is sometimes possible on repeated daily exposure, such as on school buses or on long-distance trips^{Footnote 73}.Such events appear to be rare, involving highly infectious cases and specific environmental circumstances (e.g. daily travel on a crowded long-duration school bus route in winter). There is no evidence to support contact tracing related to local public transportation, particularly given the logistic hurdles and considerable inefficiency of contact tracing in these circumstances^{Footnote 73}.

Possible Contact with Infectious TB Cases During Residence or Travel in a Country with High TB Incidence

Refer to Chapter 13, Tuberculosis Surveillance and Screening in Selected High-Risk Populations.

Management of a TB Outbreak

TB outbreaks generally last for several years; response and control are major undertakings^{Footnote from 74 to 7674-76}. In addition, outbreaks are more likely to occur in already challenging settings, such as homeless, impoverished, or other marginalized populations, isolated Inuit or First Nations communities, etc^{Footnote 44 Footnote 54}

Definition

The definition of an outbreak of any disease is the occurrence of more cases in a given population than expected in a given time. Spatial or temporal associations may suggest ongoing transmission and an outbreak. TB outbreaks may be identified only retrospectively, after cases have been found to be linked epidemiologically or by genetic analysis. Any such clustering within the last 2 years should suggest a possible outbreak and prompt further investigation.

The following working definition of outbreak for planning investigations is based on that proposed by the U.S. Centers for Disease Control and Prevention:^{Footnote 22}

• During and because of a contact investigation, two or more of the identified contacts are diagnosed as secondary cases of active TB; or
• Any two or more cases occurring within 1 year of each other are discovered to be linked, but the linkage is recognized outside of a contact investigation. For example, two patients who received a diagnosis of TB independently, outside of a contact investigation, are found to work in the same office, yet they were not previously identified as contacts of each other. A more extreme example is when a second generation of transmission has already occurred at the time an index case is diagnosed - i.e. secondary cases have already generated their own secondary cases. The linkage between cases should be confirmed by genotyping results if cultures are available.

This definition emphasizes the pace of secondary cases occurring and the ability of the TB program to keep up with multiple contact investigations. In practice, the ability of the local TB program to manage a growing cluster of TB cases and the concurrent contact investigations in a timely way, within its usual operations, is also a key factor in determining whether or not to consider the situation an outbreak for response purposes. Most situations that have been recognized as TB outbreaks involve chains of many more than two secondary cases, or one previously unrecognized link to a secondary case, and extend over several years. The above definition is an operational one intended to help identify and contain rapidly evolving clusters. Note that a slower cluster of linked cases that spans several years may still require heightened TB program response for an identifiable population group yet not be an "outbreak" by the above definition.

Goals

The goals of the investigation and management of an outbreak of TB are as follows:

• to promptly identify the source case or cases, so that the risk of ongoing transmission of infection is rapidly reduced by isolation and initiation of appropriate treatment
• to rapidly identify new cases of active TB within the at-risk population, and initiate airborne isolation and treatment
• to identify people with recently acquired LTBI, so that preventive therapy can be given before active disease develops.

Managing an Outbreak

Organization and resources

Given the scale and duration of most TB outbreaks, it is important that there be adequate staffing and resources for investigation and management from the onset of the response efforts. Assistance from outside the TB program may be necessary. Advice from experienced colleagues who have managed TB outbreaks elsewhere can be invaluable.

The following components are recommended in any TB outbreak response:

• an identified outbreak manager, appointed for the duration, with overall responsibility for management and coordination of the outbreak response;
• public health/TB control staff to register and case-manage patients with TB, define infectiousness, coordinate the investigation and provide consultation and communication with those in the field;
• sufficient field staff to carry out the contact investigation and follow-up; for outbreaks dispersed across remote communities, mobile specialized teams may be an effective strategy to support local staff;
• information technology (IT)/database and epidemiologic support;
• consistent, coordinated clinical and diagnostic supports with expertise in TB; prompt, local access to chest radiography of adequate quality, identified medical consultants with expertise in TB to review chest radiology, evaluate patients for TB, hospitalize if necessary, and manage suspected cases and contacts in a consistent manner, without delay; for remote communities telemedicine links (including review of digital radiology) can be extremely effective, hospital facilities that can offer airborne isolation rooms, diagnostic examinations and treatment without delay, links to public health laboratories for specialized supports (arrangements to handle larger numbers of specimens, fingerprinting, etc.), rapid and safe transportation of specimens and, if necessary, patients;
• sufficient case-management and DOT staff to provide supervision of the complete course of drug treatment for all active cases - at least 1 year's additional staffing after the outbreak is over may be required;
• communications personnel to provide regular updates to the media and community on the status of the investigation;
• staff and resources to carry out the evaluation.

Roles and responsibilities

It is crucial, from the onset of the investigation, that the roles of all those involved in the investigation and management are clearly defined. Establishing an outbreak coordinating group, including the key individuals from public health/TB control, clinical expert care, hospitals, laboratory, the affected community and communications, can be very helpful. Collaboration and regular feedback among all levels of health care are important. There should be clear agreement to be followed in the investigation and the management of suspected cases and contacts, and written protocols.

Communication with health care providers

Local health care providers, particularly those who are most likely to first see new cases of TB in the outbreak population (emergency room, primary care in the outbreak neighbourhood, etc.) are key partners. Presentation at medical rounds, written notification about the outbreak and other ongoing communication will help to raise the index of clinical suspicion for TB, provide up-to-date information about TB diagnosis and management, and help decrease barriers to care, including early hospitalization for suspected infectious cases when necessary.

Staff training

Given the scale of TB outbreaks and response, many staff involved may not be experienced in TB work; including training and education/clinical rounds at all the organizations involved in the response plan can be helpful.

Prompt isolation and treatment of cases of active disease

An outbreak should markedly raise the index of clinical suspicion for TB when anyone in the affected community presents with compatible symptoms, particularly for respiratory (i.e. infectious) TB. All suspected infectious cases should be promptly isolated - in hospital if necessary - and investigated to confirm the diagnosis and the degree of infectiousness. Suspect cases should not return to congregate settings until infectious TB has been ruled out.

Case-finding, identification of source case, and contact investigation

In outbreaks among homeless and other marginalized populations, outreach street nursing, primary care clinics on site at shelters or other homeless services, and other low-threshold types of care are often critical for early diagnosis^{Footnote 44,Footnote 75,Footnote 75,Footnote 76}. Shelter staff may be the first to identify an ill resident; training about TB and infection control precautions, basic symptom screening on admission, and mechanisms to rapidly isolate and refer suspect TB cases for medical evaluation should be implemented.

If not apparent, the source case or cases should be identified through aggressive investigation of all symptomatic individuals in the at-risk community. Once the initial investigation is under way, a review of the history of TB in the community is important. Review of "old cases" by provincial/territorial and local public health/TB programs may identify previously inadequately treated cases. In some circumstances it may be helpful to locate and reassess previously identified high-risk contacts who were lost to follow-up or did not take or complete treatment for LTBI.

In small communities or in closed settings it may be more efficient to screen the entire community or those in the facility at baseline, especially as it may be difficult to determine the exact level of contact in a small, close-knit community. In some settings, especially if members are very mobile, offering on-site active case-finding (sputum and/or chest radiography as well as symptom screening) on an ongoing basis over an extended period of time may be the only way to ensure that most contacts are identified and screened ^{Footnote from 53 to 55 53-55, Footnote from 75 to 77 75-77}. Many remote communities have members who travel back and forth frequently to other communities; tracking these individuals is particularly difficult, yet they can be a conduit to spread the outbreak to additional communities. Coordination and shared follow-up arrangements with TB programs in these other communities may be very helpful in the assessment and management of mobile contacts and cases.

In populations in which treatment of LTBI is not realistic as a major outbreak control strategy, the primary emphasis should be on early detection and treatment-to-cure of active cases, rather than extensive efforts to do skin testing. Examples include elderly residents (over 65 years) in long-term care facilities and some homeless populations (e.g. older alcoholics). Also, refer to Chapter 15.

A heightened index of clinical suspicion and perhaps case finding efforts should be maintained for several years after the outbreak subsides, as there is usually a pool of recently infected people remaining in the community. It may be possible to follow infected contacts who refuse or are not eligible for treatment of LTBI in order to detect early TB disease (e.g. periodic clinical assessment for 2 years after exposure).

Data management and epidemiologic support

Contact investigation and management in a TB outbreak is very data-heavy. Tracking hundreds of contacts, often through multiple sites and assessments, demands a good database and IT support. Rapid, thoughtful evaluation of the aggregate results as they become available requires a dedicated epidemiologist.

Identify fundamental causes

TB outbreaks mainly take place in settings where rapid transmission is possible - inadequate housing (overcrowding, inadequate ventilation) and prolonged infectiousness often related to limited health care access. A high prevalence of vulnerability factors among contacts accelerates the development of secondary cases: the presence of many young children, diabetes and other causes of immunosuppression, smoking, malnutrition, etc. In facility-based outbreaks (homeless shelters, hospitals, jails) a systematic assessment of conditions and practices, including ventilation, may identify areas for intervention (also, refer to Chapter 15). Individual cases can be treated and cured, but it is very difficult to contain outbreaks or reduce endemically high rates of TB without addressing the fundamental causes. These aspects, too, should be recognized, and when possible addressed in the outbreak response.

Community outreach and education

TB outbreaks can be anxiety-provoking and stigmatizing. Often they take place in a context of limited or inaccurate information about TB and sometimes quite negative cultural/historical associations. All these can prolong the situation through delayed diagnosis if individuals either do not recognize the significance of their symptoms or are afraid to receive a diagnosis of TB. It is crucial to provide information about TB and the outbreak response to the affected community or setting as early as possible in the investigation of the outbreak, with regular updates for them and for the general local population. The information should be in a style and format that is accessible and takes into account the cultural and practical setting of those affected. Standard materials may need to be adapted, ideally with input from community members. Peer outreach may be very useful, particularly for hard-to-reach individuals. This will help reduce the level of anxiety and will likely lead to greater cooperation and adherence to recommendations.

Evaluate the process and outcome of the outbreak investigation

Ongoing evaluation and a formal evaluation at the end of the outbreak, including both the process and outcome of the outbreak investigation, are crucial. DNA genotyping of isolates may be useful in identifying the presence of an outbreak, mapping its extent and evaluating the results of the outbreak investigation and control. Identification of key contributing factors, often social determinants of health, may point to future non-TB-specific interventions.

 

References