Volume 28-16
15 August 2002

[Table of Contents]

PNEUMONIA EPIDEMIC CAUSED BY A VIRULENT STRAIN OF STREPTOCOCCUS PNEUMONIAE SEROTYPE 1 IN NUNAVIK, QUEBEC

Nunavik is the most northerly health and social services region in Quebec. Approximately 90% of the population of about 10,000 is Inuit and inhabitants are spread over 14 communities. Half the population is < 20 years of age and there are about 275 births per year. Respiratory disease is hyperendemic. In 1999-2000, the Nunavik rate of hospitalization for pneumonia from all causes was 23.8 per 1,000, compared to 4.2 per 1,000 for the Quebec population as a whole. From 1997 to 2001, 22 invasive strains of Streptococcus pneumoniae were isolated, yielding an average annual rate of 54 per 100,000 – three times higher than for the whole province⁽¹⁾. The difference might actually be much greater, considering the difficulties obtaining blood samples to culture. The distribution of bacterial serotypes in patients >= 5 years of age shows that the majority (eight of nine) are covered by 23-valent polysaccharide vaccine (all nine with cross-immunity for serotype 6A). In children < 5 years of age, seven of the 11 serotyped invasive strains are covered by the 7-valent conjugate vaccine (10/11 with cross-immunity for serotypes 6A and 19F). Otitis is a huge problem and by 5 years of age, one quarter of the children have hearing loss⁽²⁾. A 1997 study in one community revealed a 61% prevalence of eardrum abnormalities⁽³⁾. In the early 1990s, a vaccination program was conducted with 23-valent polysaccharide vaccine for individuals >= 65 years of age, and those > 2 years of age at high-risk of invasive infection. Coverage rates were estimated to be > 80% in the first group and < 40% in the second.

In November 2000, a cluster of acute pneumonia cases in young adults was reported in one Nunavik community. A retrospective analysis of medical files was undertaken throughout the region to document the outbreak characteristics, and an active surveillance system was established to monitor the course and identify its etiology. A standard survey  form was used to document each acute pneumonia case, which was defined as sudden onset of fever, accompanied by a respiratory symptom (cough, dyspnea, or pleuritic pain), and requiring admission to a clinic or hospital for intravenous antibiotic treatment. Nursing staff were asked to take blood, urine and sputum samples for culture, as well as serology and antigen detection tests. Active surveillance was suspended in March 2001, but reactivated in September when outbreak resumption was confirmed.

In all, 84 severe pneumonia cases were identified, 43 during the first phase of the outbreak from August 2000 to February 2001 affecting eight communities, and 41 cases during the second phase beginning in August and ending in December 2001 affecting 11 communities, most of which had not been affected during the first phase. All age categories were affected, with the highest attack rate in the < 1 year age group (23/1,000) and the >= 65 years age group (31/1,000). However, an unusual percentage of cases (34/84, or 40%) occurred in adults aged 20 to 64 years. The severity of the cases is evidenced by the fact that hospitalization was required for 75 patients, 18 of whom were transferred South to an intensive care centre. There was one death. A risk factor for invasive pneumococcal disease was found in 26 of 65 patients for whom information was available (usually a chronic respiratory pathology). It should be noted that 13 patients had a history of immunization with 23-valent polysaccharide vaccine.

The results of the various diagnostic tests are shown in Table 1. The serology tests and sputum cultures should be interpreted with caution, however the results are consistent with the blood culture results in revealing the dispersion of a virulent strain of S. pneumoniae serotype 1. Ten strains of serotype 1 were analyzed by pulsed field gel electrophoresis. They shared a common profile, similar to that of the invasive serotype 1 strains in patients in Nunavut, but very different from the profile of isolated serotype 1 strains in patients living in the Montreal and Estrie areas. Serotype 1 is rare in Quebec, with only 14 cases reported out of 1,840 strains serotyped from 1996 to 1999⁽¹⁾. In 2000 and 2001, 12 of the 17 serotype 1 strains isolated in Quebec came from Nunavik. One confirmed-case (by blood culture) of invasive S. pneumoniae serotype 1 occurred in a patient, 65 years of age, who had been vaccinated in 1995 and was suffering from chronic obstructive lung disease.

Table 1.    Results of diagnostic tests, in hierarchical order, among 84 patients with severe pneumonia in Nunavik, 2000-2001

*    Greater than three-fold increase in serum concentration of specific IgG antibodies, assayed using the ELISA test, the first serum samples taken during the acute phase of the disease and the second during convalescence.

There was a single study found which documented the successful use of 23-valent polysaccharide vaccine to control an epidemic caused by a serotype 1 strain in a community in Israel⁽⁴⁾. A mass immunization campaign was launched using this vaccine, targeting the entire population >= 5 years of age. The campaign started in April 2002 and will end in June. As well, a routine newborn vaccination program with 7-valent pneumococcal conjugate vaccine began in April 2002, along with catch-up for children < 5 years of age. The impact of these interventions on the epidemiology of pneumococcal diseases, respiratory infections in general, and otitis and their sequelae, will have to carefully assessed. The 7-valent conjugate vaccine, currently available in Canada, does not contain serotype 1. However, serotype 1 is contained in the 9-valent and 11-valent conjugate vaccines currently in development⁽⁵⁾. The prompt introduction of these new vaccines would be a positive development.

Acknowledgements

We wish to thank the clinical and laboratory personnel and records staff at the Centre de santé Tulattavik de l’Ungava and the Inuulitsivik Health Center who reported the outbreak and then supported the clinical and microbiological investigation. Outside of Nunavik, we wish to acknowledge the expertise and cooperation of: Michel Couillard of the Quebec Public Health Laboratory, François Lamothe, microbiologist and infectious diseases specialist at the Hôpital Saint-Luc de Montréal, Jeannette Macey of the Field Epidemiology Training Program, Ann Roberts of the Nunavut Department of Health and Social Services, Margareth Lovgren of the National Centre for Streptococcus in Edmonton, Daniel Sikkema of Wyeth-Ayerst Laboratories, Rochester, New York, and the Laval University Regional Virology Laboratory.

References

1. Jetté LP, Delage G, Ringuette L et al. Surveillance of invasive Streptococcus pneumoniae infection in Quebec, Canada, from 1996 to 1998: serotype distribution, antimicrobial susceptibility, and clinical characteristics. J Clin Microbiol 2001;39:733-37.
2. Hodgins S. Health and what affects it in Nunavik: how the situation is changing. Kuujjuaq, Quebec: Nunavik Regional Board of Health and Social Services, 1997.
3. Bruneau S, Ayukawa H, Proulx JF et al. Longitudinal observations (1987-1997) on the prevalence of middle ear disease and associated risk factors among Inuit children of Unukjuak, Nunavik, Quebec, Canada. Int J Circumpolar Health 2001;60:640-48.
4. Dagan R, Gradstein S, Belmaker I et al. An outbreak of Streptococcus pneumoniae serotype 1 in a closed community in Southern Israel. Clin Infect Dis 2000;30:319-21.
5. National Advisory Committee on Immunization (NACI). Statement on recommended use of pneumococcal conjugate vaccine. CCDR 2002;28(ACS-2):1-32.

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