Rubella Outbreak among Office Workers -- New York City

In 1984, a provisional total of 745 rubella cases was reported in the United States. This is a 23.2% decrease from the 1983 total (970 cases) and a 98.7% decrease from the 1969 total of 57,686 cases, the highest number ever reported. The 1984 figure represents a new all-time low. However, rubella cases continue to occur among susceptible adults, particularly childbearing-aged women. While colleges and universities have traditionally been recognized as sources for rubella outbreaks because of pooling of susceptibles (1), the outbreak presented below demonstrates that rubella transmission can and does occur in the work setting if enough susceptible young adults are closely confined.

Sixty-nine cases of rubella* involving workers in two exchanges and two brokerage firms in the financial district of lower Manhattan were reported to the New York City Department of Health between March 20 and June 5, 1984 (Figure 2). Two other cases were identified in contacts who did not work in the financial district. Twenty-seven (38.0%) of these 71 cases were serologically confirmed.

Of the 69 cases in the financial district workers, 42 (60.9%) involved workers at Exchange A; 18 (26.1%) were in workers at Exchange B; and nine (13.0%) involved employees at two brokerage firms. The two other cases were in contacts of patients from Exchange A. Epidemiologic links were demonstrated between the two exchanges and between Exchange B and the two brokerage firms.

Because the work force at the two exchanges includes exchange employees, several hundred exchange members, and member firms and their employees, the total number of persons at risk at the exchanges during the outbreak and their age and sex distributions are unknown. Therefore, the denominators used in calculating attack rates are estimates by exchange officials of the total population at risk. Based on these estimates, the overall attack rate for Exchange A (21 cases per 1,000 workers) was significantly higher than that for Exchange B (6/1,000) (p 0.001).

Forty-nine (71.0%) of the 69 cases occurred among men (male-to-female ratio = 2.5:1). Of these 69 primary cases, 55 (79.7%) involved patients under 30 years of age. The median age of patients was 25 years (Figure 3).

The estimated attack rates for male and female employees in the two exchanges (13.8/1,000 and 8.4/1,000, respectively) do not differ significantly, nor do the estimated attack rates for all workers by age (Table 4). However, men under 30 years of age had the highest observed attack rate (16.7/1,000), and their risk of infection was significantly higher than that for women of the same age (7.7/1,000) and that for older men (7.0/1,000) (p 0.05).

No patient was known to have been previously immunized against rubella. No pregnant women were known to have contracted rubella during the outbreak.

To control the outbreak, 1,639 workers, approximately one-third of the work force, were vaccinated at the two exchanges in separate vaccination clinics sponsored by the New York City Department of Health. Separate vaccination programs sponsored by employee health units were conducted at the two brokerage firms. Women of childbearing age were counselled about the theoretical teratogenicity of live-virus vaccines and advised to avoid pregnancy for 3 months after vaccination. Additionally, serum specimens were voluntarily collected before vaccination from approximately 80% of these women and stored so that a prevaccination rubella titer could be determined for any women who subsequently became pregnant. Two women became pregnant, both 22 weeks after vaccination: one proved to be seropositive before vaccination, and the other had refused to have blood drawn. Each woman delivered a normal child. No adverse results of vaccination--including absenteeism--were reported. Reported by GS Alkaya, MD, RM Hockberg, Executive Health Examiners, Inc., J. Thompson, Commodities Exchange Center, Inc., AP Nazitto, LA Pizzurro, FF Schady, MA McPherson, RL Coshnear, Div of Immunization, AK Goodman, MD, SM Friedman, MD, S Schultz, MD, Bureau of Preventable Diseases, ST Beatrice, PhD, SJ Millian, PhD, Bureau of Laboratory Svcs, DJ Sencer, MD, Commissioner of Health, New York City Dept of Health; Div of Field Svcs, Epidemiology Program Office, Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: This is the third reported rubella outbreak involving office workers in the United States and the second in New York City (2,3). The previous New York outbreak involved 86 cases among workers at a major bank in the financial district of lower Manhattan (3). In that outbreak, attack rates were significantly higher for women than for men and were higher for women under 45 years of age than for women 45 years old and older. In the 1984 outbreak, the overall attack rate for men was higher than that for women, although not significantly so. The difference may in part be due to the fact that the denominator data in the latest outbreak were only estimates. In both outbreaks, however, attack rates were higher for younger workers than for older workers; this finding is consistent with the estimated 10%-15% prevalence of seronegative young adults (4). This remaining susceptible cohort is a result, not of vaccine failure, but of failure to be vaccinated. Available data indicate no appreciable decline in vaccine-induced immunity over time, regardless of the rubella vaccine strain (4,5).

Outbreaks lead not only to disruption of the workplace and time lost through illness but also to potential infection of pregnant women. Although no pregnant women were infected during this outbreak, three were infected in the 1983 New York City outbreak (3). Two subsequently had therapeutic abortions, and one delivered an infant with congenital rubella syndrome (CRS).

Rubella outbreaks will likely continue to occur in the workplace until all workers are immune. Direct vaccination of the remaining susceptible adult population could immediately reduce the risk of outbreaks in this setting. This approach is consistent with the national goal to hasten the elimination of CRS from the United States (6). The Immunization Practices Advisory Committee (ACIP) recommends that ascertainment of rubella immune status and the availability of rubella immunization be components of the health-care program in places where women of childbearing age congregate or represent a significant proportion of the work force (4). Since voluntary programs have generally been less successful than mandatory programs, the latter are preferable.

Introduction of rubella into a population should be prevented, since outbreak control may not lead to immediate termination of cases. Once infection is introduced into a susceptible population, prompt outbreak control is necessary (4). To control rubella outbreaks in the workplace, and to prevent workplace-associated CRS, active identification and confirmation of cases, exclusion of patients during the infectious period, exclusion of nonimmune pregnant women until the end of the outbreak, and vaccination of susceptibles are necessary.

While prevaccination blood specimens were obtained from women in this outbreak, this practice is not necessary, even in the nonoutbreak situation (4). The ACIP recommends vaccination if an individual simply lacks documentation of either prior vaccination on or after the first birthday or serologic evidence of immunity. For females without such evidence of immunity, one should simply ask the woman if she is pregnant or believes she might become pregnant in the next 3 months. If she says she is not, she should be vaccinated after discussing the need to avoid conception for the ensuing 3 months. All available data indicate that vaccination of immune individuals is not associated with any increased risk of adverse events and that the risks to the fetus following exposure to the vaccine virus are negligible (4,5).

References

1. CDC. Rubella in colleges--United States. MMWR 1985;34:228-31.

2. CDC. Rubella outbreak in an office building--New Jersey. MMWR 1980;29:517-8.

3. CDC. Rubella outbreak among office workers--New York City. MMWR 1983;32:349-52.

4. ACIP. Rubella prevention. MMWR 1984;33:301-10,315-18.

5. Preblud SR. Some current issues relating to rubella vaccine. JAMA 1985;254:253-6.

6. CDC. Elimination of rubella and congenital rubella syndrome -- United States. MMWR 1985;34:65-6. *Generalized maculopapular rash and at least one of the following: fever, conjunctivitis, coryza, joint pain or swelling, headache, or lymphadenopathy.

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