Influenza outbreak in an Ontario long-term care home - January 2005

Canada Communicable Disease Report

1 November 2006

Volume 32

Number 21

R Mitchell, MHSc (1), V Huynh, RN (1), J Pak, RN (1), S Thompson, RN (1), AL Noseworthy, MD, MHSc, FRCPC (1)

  1. Haliburton, Kawartha, Pine Ridge District Health Unit, Ontario

Introduction

On 24 January, 2005 the Haliburton, Kawartha, Pine Ridge District Health Unit was alerted by a long-term care home (LTCH) of a possible respiratory outbreak. Five residents had displayed sudden onset of fever and two residents had been hospitalized. At the time the Health Unit was alerted, the home's resident population was 139 and there were 175 staff. During October and November 2004, residents were immunized using the same influenza vaccine, Fluviral®, lot number 3FV2O711. Influenza vaccination coverage rates were 85% for residents and 84% for staff.

This report summarizes the findings from the investigation, which confirmed that A/California/7/2004-like (H3N2) strain was circulating in the home. The Health Unit in partnership with the staff in the home investigated 74 resident cases and 55 staff cases and implemented an outbreak response plan.

Methods

Case definition

Cases of influenza in the home were identified using the following case definition: any resident or staff member with laboratory confirmation of influenza having onset date on or after 10 January, 2005 or any resident or staff member who had two or more of the following symptoms having an onset date on or after 10 January, 2005: fever, tiredness, muscle aches, joint pain, loss of appetite, headache, chills, runny nose or sneezing, stuffy nose (i.e. congestion), sore throat or hoarseness, difficulty swallowing, cough, swollen or tender glands in the neck, chest tightness or shortness of breath.

Case finding

A standard data collection tool was used to collect information for residents and staff who met the case definition. Data collected for residents included demographic information, symptoms, prophylaxis, vaccination, underlying medical conditions, antibiotic use, hospitalization, death, and in-house transfers. Data extraction from charts was undertaken for ill residents at the home. Data collected for staff included the above variables as well as whether they sought medical attention, ill household members, work schedule prior to onset of symptoms and employment at other health care facilities. Data were also collected from ill staff via telephone interviews.

Statistical analysis

Data were entered into EpiData version 3.1 and analyzed in SPSS version 12.0. Descriptive statistics were used to describe age, symptoms, vaccination rates, hospitalization and death.

Attack rates were calculated as follows: the number of resident or staff cases divided by the total number of residents or staff members respectively, multiplied by 100.

The case fatality rate among residents was calculated as follows: the number of residents who died due to influenza divided by the number of resident cases, multiplied by 100.

Public health measures

Upon notification of the respiratory outbreak the Health Unit, in accordance with the document entitled “A Guide to the Control of Respiratory Infection Outbreaks in Long Term Care Homes 2004”1, advised the home to follow appropriate restrictions on admissions and transfers as outlined in the above-mentioned document. The Health Unit reviewed the above guidelines with the home to ensure that they were appropriately implemented. The Health Unit also recommended that the home implement respiratory outbreak control measures including respiratory isolation, limiting transfer of residents between units, enhanced hand washing and environmental sanitation, and barrier precautions for all ill residents. In addition, prior to laboratory confirmation of influenza, as a precaution the home's management did not allow unvaccinated staff to work. Once laboratory confirmation was received for influenza A, the Health Unit recommended that treatment and prophylaxis commence based on the “A Guide to the Control of Respiratory Infection Outbreaks in Long Term Care Homes 2004”1.

Laboratory investigations

Five nasopharyngeal (NP) swabs were obtained from ill residents and sent to the Public Health Laboratory on 25 January, 2005 for rapid test and virus culture. During the course of the investigation, 14 specimens were sent to the Public Health Laboratory. Testing included tissue cultures and polymerase chain reaction (PCR) testing for influenza A, influenza B, RSV, Chlamydia pneumonia, Mycoplasma pneumonia and adenovirus. Two isolates were sent to the National Microbiology Laboratory in Winnipeg for strain characterization on 17 February, 2005. No specimens were collected from staff at the home, however two staff submitted NP swabs to their physician when they sought medical attention.

Results

The epidemic curve of the influenza outbreak is shown in Figure 1.

Residents

As of 21 February, 2005, 74 residents met the case definition.

The attack rate among residents was 53% (74/139). The median age of resident cases was 85 years (range: 46 to 105 years). The vaccination rate among resident cases (n = 59) was 80%.

Antivirals were initiated for 93% (69/74) residents on 28 January, 2005.

Figure 1. Epidemic curve, influenza A outbreak, Cobourg, Ontario, 10 January, 2005 - 21 February, 2005

Figure 1. Epidemic curve, influenza A outbreak, Cobourg,Ontario, 10 January, 2005 - 21 February, 2005

Three residents were diagnosed with pneumonia; two of the three were confirmed by chest x-ray. Fourteen of the resident cases were hospitalized.

On 30 January, 2005 the first influenza related death was reported to the Health Unit. During the course of the outbreak, 11 residents died from influenza-related illnesses and a further 11 residents died from other causes. The case fatality rate was 15% (11/74). The median age of the residents who died from influenza-related illness was 89 years (range: 79 to 97 years) and 91% (10/11) of the residents who died from influenza-related illness were vaccinated.

Staff

As of 21 February, 2005, 55 staff members met the case definition.

The attack rate among staff was 31% (55/175). The median age of staff cases was 47 years (range: 21 to 61 years). Forty per cent of staff cases worked as healthcare aides (n = 22), 18% worked as Registered Practical Nurses (n = 10) and 18% worked in the dietary department (n = 10). The vaccine coverage rate was 93% (51/55) among staff cases.

Unvaccinated staff that chose to continue working at the home during the outbreak were put on antivirals on 26 January, 2005. Half (53%) of staff cases sought medical attention for their symptoms. One staff case was hospitalized due to pneumonia on 7 February, 2005 for one day. Less than half (42%) of staff cases reported household members who were also ill. There were no fatal cases of influenza among staff.

Figure 2. Frequency of influenza symptoms

Figure 2. Frequency of influenza symptoms

It was reported that staff worked on more than one floor in the home. As well, five staff cases were employed in other acute and long-term care homes. No transmission to these homes was reported.

Figure 2 summarizes staff and resident symptoms.

Laboratory investigations

On 25 January, 2005 the Public Health Laboratory reported that all five specimens were negative for influenza A, B and RSV using the rapid test (enzyme-immunoassay). On 28 January, 2005 the Public Health Laboratory confirmed a specimen positive for influenza A through virus culture. In total, the Public Health Laboratory confirmed six specimens positive for influenza A through virus culture. The National Microbiology Laboratory in Winnipeg identified A/California/7/2004-like (H3N2) from the two isolates, reported to the Health Unit on 24 February, 2005.

The results from specimens submitted by staff through local physician were negative for influenza A, B and RSV.

Discussion

The respiratory outbreak at the LTCH began on 10 January, 2005 and was declared over on 21 February, 2005. Influenza vaccination coverage rates were 85% for residents and 84% for staff. Despite the high vaccination rates the attack rate for residents and staff were 53% and 31% respectively. The case fatality rate for residents was 15%.

There are several factors that could explain the morbidity and mortality associated with this outbreak. Not unexpectedly, these deaths occurred among an elderly and medically compromised population who had an average age of 88 years. This home had a greater proportion of medically frail, elderly residents as compared to other LTCHs within the same geographic region. According to the National Advisory Committee on Immunization (NACI), during the 2004-2005 season influenza had a significant impact on LTCHs in Canada. The total number of outbreaks in LTCHs reported in 2004-2005 exceeded the total number of LTCH outbreaks in any of the last three seasons2. As well, laboratory results indicated that A/California/7/2004-like (H3N2) was circulating in the home. The 2004-2005 influenza vaccine did not contain this strain, however the Public Health Agency of Canada stated that there was cross reactivity and the 2004-2005 vaccine would have provided some protection3, but due to the antigenic difference, effectiveness of the 2004-2005 vaccine would have been reduced2. However, even with reduced vaccine efficacy, immunization still provides an opportunity to reduce morbidity and mortality associated with influenza.

Outbreak detection and confirmation of diagnosis are two essential steps in an outbreak investigation. Early detection of influenza infection in the elderly poses a challenge for surveillance, and as illustrated in Figure 1, the Health Unit was not notified until the peak of the outbreak. Therefore, more timely notification to public health might have facilitated the prompt implementation of control measures, thereby reducing the spread of infection throughout the home. As well, the confirmation of influenza may have been delayed because of to the expired medium in which the first specimens were contained as well as the lack of sensitivity of the rapid test.

Conclusions

This investigation concluded that A/California/7/2004-like (H3N2) was circulating within the long-term care home among a population of elderly and medically frail residents. This outbreak lasted 43 days and had an impact not only on the residents and staff at the home, but the entire community. This experience points out a need for the following:

  • Strengthening the training provided to LTCH staff in conducting surveillance for respiratory symptoms of both residents and staff.
  • Ensuring that all expired specimen collection kits are removed from LTCHs during the Health Unit's annual influenza visit.
  • Ensuring that appropriate specimen collection and transport occurs according to the Ministry of Health's “A Guide to the Control of Respiratory Infection Outbreaks in Long Term Care Homes 2004”1.
  • Improved laboratory access to reagents when new strains are suspected during an outbreak.
  • Improved communication of patient status and infection control procedures during an outbreak between LTCHs, the Health Unit, hospitals and other local health professionals.
  • To continue to promote annual influenza vaccination for all residents and staff in LTCHs to reduce and prevent morbidity and mortality associated with influenza.

Acknowledgements

The authors would like to thank the following for their assistance in the outbreak investigation: the staff at the LTCH, Cobourg, Ontario; the Northumberland Hills Hospital, Cobourg, Ontario; the Public Health Laboratory, Peterborough, Ontario; Dr. E. Bontovics, Ministry of Health and Long-Term Care, Toronto, Ontario; Dr. G. Broukhanski, Central Public Health Laboratories, Etobicoke, Ontario; Dr. T. Tam, Public Health Agency of Canada, Ottawa, Ontario; C. Navarro, Canadian Field Epidemiology Program, Public Health Agency of Canada, Ottawa, Ontario; and the National Microbiology Laboratory, Winnipeg, Manitoba. Critical appraisal of the manuscript: Diane Dingman, Linda McCarey and Anne Marie Holt, Haliburton, Kawartha, Pine Ridge District Health Unit.

References

  1. Public Health Division and Long-Term Care Homes Branch, Ministry of Health and Long-Term Care. A Guide to the Control of Respiratory Infection Outbreaks in Long Term Care Homes 2004. October 2004.

  2. National Advisory Committee on Immunization (NACI). Statement on influenza vaccination for the 2005-2006 season. CCDR 2005;31(ACS-6):1-32.

  3. Public Health Agency of Canada. Flu Watch Report February 13 to February 19, 2005. URL: http://www.phac-aspc.gc.ca/fluwatch/04-05/w07_05/index.html. Date of access: 5 May 2005.

Page details

Date modified: