Measles in a Population with Religious Exemption to Vaccination -- Colorado

On July 24, 1985, a 17-year-old camper at a Colorado camp attended by Christian Scientists developed measles. She had become infected while traveling in California during the 2 weeks before her arrival at the camp. Twenty-five counsellors and 110 campers, aged 14-25 years, attended the camp; all were unvaccinated, and all were exposed to the index patient. At the time the index patient was diagnosed with measles, the exposed campers and counsellors were not yet infectious. After discussions with state health officials, it was decided that quarantining the campers and staff at the facility would be impractical for medical and logistical reasons, since the camp is located in a remote part of Colorado with minimal nearby medical facilities. Therefore, the camp was closed July 27, before any secondary cases occurred.

The campers and staff were from 24 different states. All were placed under quarantine orders in their home states, and vaccination of family contacts was offered through state health departments. Few of the families accepted immunization.

A total of 50 associated cases occurred. In the second generation, 31 campers and three counsellors residing in 15 states developed measles, an attack rate of 25.2% (Figure 3). The mean age of these patients was 14.6 years. In the third generation, 16 cases were reported from eight states. All were in unimmunized household contacts. No spread to the general community was documented. No serious complications, hospitalizations, or deaths were reported. Overall, California reported the largest number of cases (16 (31.4%)); Colorado reported six (11.8%). Reported by Immunization Program, S Ferguson, PhD, State Epidemiologist, Colorado Dept of Health; Div of Field Svcs, Epidemiology Program Office, Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: The high attack rate (25.2%) in this camp population reflects the rapidity of transmission and high susceptibility of unimmunized persons. Usual control methods consisting of timely immunization of susceptible contacts were not possible in this situation because of the religious beliefs of the campers and their families. Quarantine efforts by individual state health departments and cooperation by families of campers were apparently successful in limiting spread of disease into the community. In an outbreak among Christian Scientists at Principia College earlier this year, quarantine at the school was used as a control measure. Although transmission was sustained for at least 4 generations, there was no spread to the community (1).

The cost of controlling the camp outbreak was borne primarily by the camp, which lost approximately $106,000 in income from cancellation of an entire session, and by parents, who in many cases had to cancel other summer plans to accommodate the quarantine. Furthermore, state health departments in 16 states had to implement control measures to ensure that the measles cases imported into their states did not become foci of other outbreaks.

Although persons unvaccinated because of religious exemptions comprise a small proportion of the total population, such persons are at increased risk of acquiring vaccine-preventable diseases and may account for a large proportion of serious measles-associated complications. For example, all three reported measles-related deaths in 1985 occurred during the measles outbreak at Principia College.

Persons with religious exemptions have accounted for a small percentage of the total number of reported measles cases in the United States (2). However, they may play important roles in sustaining or initiating transmission of measles. Although no spread occurred outside the religious groups in the Principia College and Colorado outbreaks, persons with religious exemptions to vaccination have developed disease that has spread to the general community. In one such outbreak this year in Montana, a person with a religious exemption was the index patient for an outbreak that involved 137 persons (3).

While most state school immunization laws allow exemptions on the basis of religious convictions, the data presented here illustrate the necessity of excluding persons with religious exemptions (as well as other unvaccinated individuals) from school and other environments in epidemic settings where contact with other susceptibles may occur. This serves both to protect their own health and to minimize transmission in the community.

References

1. CDC. Multiple measles outbreaks on college campuses--Ohio, Massachusetts, Illinois. MMWR 1985;34:129-30.

2. CDC. Measles--United States, 1984. MMWR 1985;34:308-12.

3. CDC. Unpublished data.

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