ARCHIVED - Guidelines for the Prevention and Control of Meningococcal Disease


4.0 Definitions

4.1 National Case Definition

Table 1

Confirmed Case

Invasive disease1 with laboratory confirmation of infection:

  • isolation of N. meningitidis from a normally sterile site (blood, cerebrospinal fluid [CSF], joint, pleural or pericardial fluid); OR
  • demonstration of N. meningitidis DNA by appropriately validated nucleic acid test (NAT)2 from a normally sterile site.

Probable Case

Invasive disease1 with purpura fulminans or petechiae and no other apparent cause:

  • with demonstration of N. meningitidis antigen in the CSF; OR
  • in the absence of isolation of N. meningitidis or demonstration of DNA by appropriately validated NAT2 from a normally sterile site.
1 Invasive meningococcal disease usually manifests itself as meningitis and/or septicemia, although other manifestations may be observed (e.g. orbital cellulitis, septic arthritis). Invasive disease may progress rapidly to purpura fulminans, shock and death.
2 Each jurisdiction will have a validation process for the NAT that they have in place.

Both confirmed and probable cases of IMD are notifiable at the national level. The national case definition underwent revision in 2005. The new case definition will become effective 1 January, 2006 and now includes demonstration of N. meningitidis DNA by appropriately validated nucleic acid test (NAT) from a normally sterile site. Meningococcal DNA can be found in the CSF up to 96 hours after antibiotics have been started(8).

4.2 Definitions for Public Health Management

For the public health management of sporadic cases, outbreaks and persistently elevated rates of disease, the following definitions have been developed.

4.2.1 Cases and Contacts

Tables 2 and 3 provide definitions of cases and close contacts.

Table 2: Description of Cases

Sporadic Case

A single case occurring in a community where there is no evidence of an epidemiologic link (by person, place or time) to another case.

Index Case

The first case occurring in a community.

Subsequent Case

A case with onset of illness subsequent to another case with whom an epidemiologic link can be established. This category includes co-primary cases (a person who develops illness within 24 hours of onset of illness in the index case), as well as secondary cases (a person developing illness > 24 hours after onset of illness in the index case).

An epidemiologic link can be established when a person has one or both of the following in common with a confirmed case:

  • contact with a common, specific individual (including confirmed or probable cases),
  • presence in the same location (e.g. work, school, a bar or party) at or around the same time.
Table 3: Definition of Close Contacts
  • Household contacts of a case
  • Persons who share sleeping arrangements with the case
  • Persons who have direct contamination of their nose or mouth with the oral/nasal secretions of a case (e.g. kissing on the mouth, shared cigarettes, shared drinking bottles)
  • Health care workers (HCWs) who have had intensive unprotected contact (without wearing a mask) with infected patients (e.g. intubating, resuscitating or closely examining the oropharynx)
  • Children and staff in child care and nursery school facilities
  • Airline passengers sitting immediately on either side of the case (but not across the aisle) when the total time spent aboard the aircraft was at least 8 hours (see section 7.1.4)

For public health management, cases that occur after the index case with which an epidemiologic link can be established may have acquired the disease directly from the index case or from another common source. Subsequent cases can be early, intermediate or late. Subsequent cases that occur early (within 24 hours), termed co-primary cases, most likely acquired the disease from a common source. Conversely, subsequent cases that occur after 24 hours, or secondary cases, may have acquired the disease in either fashion.

The likelihood of person-to-person transmission of meningococcal disease is related to both the nature and duration of the contact with a confirmed case. Studies carried out before the routine use of chemoprophylaxis have revealed that people who lived in the same household as an IMD case were at 500 to 1200 fold greater risk of IMD than the general population(9,10). The risk is highest in the first week after onset of illness in a case and decreases thereafter(9,11). Studies of transmission of IMD in child care facilities and nursery schools have been conflicting but suggest that there is an increased risk of secondary cases, although the risk is lower than in the household setting(9,12). Increased risk of IMD has not been shown in casual contacts of sporadic cases(13-16). Therefore school/classroom, transportation, workplace or social contacts are not considered as close contacts unless their specific relationship with the case identifies them as such (see Table 3).

Nosocomial transmission of IMD is very uncommon, especially when routine practices and (large) droplet and contact precautions are followed to prevent the transmission of IMD. In rare instances, direct contact with respiratory secretions of infected persons (e.g. during mouth-to-mouth resuscitation) has resulted in transmission to HCWs. A pediatrician in France developed IMD a week after intubating a comatose child with meningococcal disease(17,18). Therefore, HCWs are considered as close contacts if they have had intensive, unprotected contact (without wearing a mask) with infected patients (e.g. intubating, resuscitating or closely examining the oropharynx)(19).

In certain countries, such as Canada, where chemoprophylaxis of close contacts is routinely administered for sporadic cases, 0.3% to 3% of cases of meningococcal disease occur in contacts of the index case(10,11,20,21), with a median interval between the index and the secondary case of 7 weeks in one study(11). Some of these secondary cases can be attributed to failure of chemoprophylaxis (e.g. failure of administration, poor compliance, presence of antibiotic resistance)(20,22-24). “Late” secondary cases in close contacts may occur several months after the onset of symptoms in the index case(11,12).

4.2.2 Outbreaks

An outbreak is defined as increased transmission of N. meningitidis in a population, manifested by an increase in cases of the same serogroup.

Outbreaks can be subdivided into organization-based or community-based outbreaks using the criteria shown in Table 4.

Table 4: Types of Outbreak

Organization- based

Increased transmission of N. meningitidis in an organization or institution with two or more cases of the same serogroup occurring within a 4-week interval. This includes restricted populations, such as schools, day care, sports groups or social groups, as well as nursing homes or long-term care facilities.


Increased transmission of N. meningitidis in a community, with three or more confirmed cases of the same serogroup occurring within a 3-month interval AND an age-specific incidence OR specific community population incidence of approximately 10/100,000, where there is an absence of an epidemiologic link between cases. This is not an absolute threshold and should be considered in the context of other factors (see section 7.2).

When threshold incidence rates are being calculated in order to establish whether continued transmission of N. meningitidis is occurring in a community, the calculation should be specific to the situation. If the cases are occurring among persons of a specific age range, the calculation should be an age-specific incidence. However, if the population is defined geographically, the calculation should use the total community population defined by that region. For the calculations, subsequent cases among close contacts should be excluded from the numerator. Age-specific incidence should be calculated for 5-year age groups (e.g. 0 to 4 year olds, 5 to 9 year olds, 10 to 14 year olds). For example, in a community with 10 cases, of which 2 live in the same household, only 9 cases are included when calculating age-specific incidence rates for the purpose of determining whether an outbreak or ongoing transmission is occurring.

4.2.3. Persistently Elevated Rates

Persistently elevated rates of disease are observed when there is ongoing occurrence of cases of meningococcal disease of the same serogroup at rates above the expected level of disease in a given population. These cases can be sporadic or outbreak-related and continue to occur despite local public health control measures.

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