Volume 26-08
15 April 2000

[Table of Contents]

OUTBREAK OF MUMPS, MONTREAL, OCTOBER 1998 TO MARCH 1999 - WITH A PARTICULAR FOCUS ON A SCHOOL

Mumps is a vaccine preventable disease. Although the Quebec program of a combined measles, mumps, rubella (MMR) vaccine was introduced in 1976, mumps only became a notifiable disease in 1986⁽¹⁾. The coverage for children 7 years of age in the province of Quebec is estimated at 95%⁽¹⁾. Very few cases are reported each year in the Montreal-Centre Region. However, in the fall of 1998, an upsurge was noticed in the number of cases of mumps in the community and in one school in particular.

Upon indication of the increase, a letter was forwarded by the Montreal-Centre public-health unit to the Centres locaux de services communautaires (CLSC) of Montreal, to emergency rooms, and to Info-Santé (a telephone line providing medical information to the public) asking for notification of any suspected cases.

Case definitions

A confirmed case was defined as presenting clinical manifestations compatible with those of mumps (i.e. fever, painful swelling of one or more salivary glands) and the presence of one of the following conditions:

• serologic detection of IgM mumps antibodies or detection of a significant increase (at least fourfold) in IgG mumps antibodies in the serum collected during the acute phase and that collected during the convalescent phase (with an interval of at least 2 weeks between the two and with an analysis carried out in the same laboratory);
• isolation of the mumps virus;
• epidemiologic link with a confirmed case using one of the above-mentioned laboratory tests.

A probable case was defined for this outbreak was defined as presenting painful swelling of one or more salivary glands for at least 2 days and the symptoms must have appeared after 27 August 1998.

Immunization records were also checked by CLSC area school nurses.

Results

In all, 37 cases corresponded to the definition of confirmed or probable cases; 49% were male. The average age was 10.5 years (range: 0.9 to 42 years) and the median age was 8 years. School children presented with 23/37 (62%) of the cases. Half of these were from the same school. Children in four daycare centres accounted for 5/37 (14%) of the cases. In all, 59% of the cases had been vaccinated or indicated having been vaccinated. In school X, which accounted for 30% of the cases, 7/12 (58%) had not been vaccinated (the immunization status of one case was unknown). 19/37 (51%) were confirmed, eight by IgM serologic confirmation, two by means of a viral culture and nine through epidemiologic linkage. Figure 1 illustrates the epidemic curve.

Figure 1 Epidemic curve, outbreak of mumps in Montreal, October 1998 to March 1999 (n=37)

The majority of cases occurred between October and December 1998. Between January and March 1999, 11 cases were reported; only one was confirmed by serology. Serologic testing was carried out on seven of the suspect cases and six were found to be negative. It therefore appeared that the cases were parotitis caused by another type of virus and that the outbreak was over. None of the cases presented with the complications associated with the mumps virus infection.

Discussion

Mumps outbreaks have been reported in highly vaccinated populations or in populations where vaccine coverage was found to be insufficient^(2-6). In this case, school X presented a majority of cases deemed unvaccinated. During the epidemiologic survey, it was found that all of these cases were among students attending welcoming classes. Such classes are organized specifically for children who have recently immigrated to Canada. They may possibly have received measles vaccine, but without a mumps component, at an early age in their country of origin under the Expanded Programme on Immunization (EPI). It is possible that these children did not have the opportunity to be vaccinated against rubella and mumps, and are therefore susceptible to these diseases. The Quebec immunization program includes two doses of measles vaccine. The second dose should be given in the form of the combined MMR vaccine to ensure that these children would also be protected against mumps and rubella.

When the CLSC-area school nurses attempted to determine the immunization status of the children, it was found that it was unknown for almost one-third of the students at the school. This outbreak is a good example of the difficulties encountered by school nurses, especially in a multi-ethnic environment, when attempting to evaluate the immunization status of students to determine who should or should not be vaccinated.

It is possible to conclude that children born in other countries, especially in countries that have an EPI, are not necessarily protected against mumps and can constitute a reservoir susceptible to the disease and thus contribute to a possible outbreak in the community. It therefore important to verify and update, as quickly as possible, the immunization status of children at the beginning of the school year or at the time of their arrival at the school.

Acknowledgements

C. Savard, MSc, Bureau de surveillance épidémiologique, Unité des maladies infectieuses, Direction de la santé publique Montréal- Centre, C. Godin, RN, CLSC des Faubourgs.

References

1. De Serres G, Boulianne N, Buissière N et al. Epidemiology of mumps in Quebec, 1970 -1995. CCDR 1997;23:9-14.

2. Briss PA, Fehrs LJ, Parker RA et al. Sustained transmission of mumps in a highly vaccinated population: assessment of primary vaccine failure and waining vaccine-induced immunity. J Infect Dis 1994;169:77-82.

3. Cheek JE, Baron R, Atlas H et al. Mumps outbreak in a highly vaccinated school population. Arch Pediatr Adolesc Med 1995;149:774-78.

4. Hersh BS, Fine PE, Kent WK et al. Mumps outbreak in a highly vaccinated population. J Pediatr 1991;119:187-93.

5. Bell A, Bigham M, Daly P et al. Outbreak of mumps among young adults - Vancouver, British Colombia. CCDR 1997;23:169-72.

6. Wharton M, Cochi SL, Hutcheson RH et al. A large outbreak of mumps in the postvaccine era. J Infect Dis 1988;158:1253-60.

Source: A Bruneau, MD, MSc, C Duchesne, BScN, Unité des maladies infectieuses, Direction de la santé publique Montréal-Centre, Montreal, Quebec.

[Previous] [Table of Contents] [Next]