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Epidemiologic Notes and Reports Mumps in the Workplace -- Chicago
Between August 18 and December 25, 1987, 116 employees at three futures exchanges in Chicago developed clinically diagnosed mumps* (Figure 1). Three cases subsequently occurred in household contacts of affected exchange employees. Twenty-one persons developed complications; nine were hospitalized.
In September 1987, the employee health nurse at one of Chicago's four futures exchanges notified the Chicago Department of Health (CDOH) of a cluster of mumps cases among employees. Of the 119 cases subsequently identified among employees of three exchanges and their household contacts, three patients were tested for and had mumps-specific IgM antibody. Seventy-six cases occurred in persons working at exchange A; 39 cases, in persons at exchange B; and one case, in a person at exchange C.
Eighty-two (69%) of the affected exchange employees completed questionnaires. Two men at exchange A reported the onset of facial swelling on August 18. One was a 23-year-old phone clerk; the other was a 30-year-old trader working in a different area of the exchange. The first case at exchange B occurred in a 27-year-old man who had no known contact with an exchange A employee with mumps; he had onset of facial swelling on September 6. The only case at exchange C occurred in a 29-year-old woman whose facial swelling developed on October 13; she had no known contact with anyone with mumps from exchanges A or B.
Cases at exchanges A, B, and C could not be epidemiologically linked. Based on a median incubation period of 16-18 days, up to eight generations of cases occurred at exchanges A and B (Figure 1).
Because some employees work at multiple exchanges, the actual numbers of persons at risk, their ages, and their genders were not known for each of the exchanges. Based on estimates by exchange officials of the population at risk (approximately 7300 persons at each of exchanges A and B), the crude attack rate for exchange A (10 cases/1000 workers) was twice that of exchange B (5 cases/1000 workers). No denominator estimates were available for exchange C.
Age was known for 104 of the 119 patients and ranged from 17 to 70 years (median: 25 years). Persons less than 30 years of age accounted for 77% of the cases. By comparison, during January-July 1987, a period of widespread mumps activity in Chicago and its six metropolitan counties, 106 cases were reported in persons greater than or equal to 20 years old. In the futures exchanges, almost twice as many men (79) as women (40) developed mumps. Of 92 patients for whom race/ethnicity was known, 84 (91%) were white, non-Hispanic, seven (8%) were black, and one was Hispanic. Although demographic data were not available for the population at risk, it was predominantly young, male, and white. Of the 99 patients for whom occupation was known, 94 (95%) worked on the trading floor.
Although more than one third of the 82 patients for whom information was available believed they had previously been vaccinated against mumps, only three could provide an immunization record as documentation. Almost three fourths of the patients had attended elementary or secondary school in Illinois, which did not have a mumps immunization law for school attendees until 1987.
In cooperation with exchanges A and B, the CDOH sponsored four voluntary vaccination clinics during the outbreak (Figure 1). Four hundred fifty-one doses of monovalent mumps vaccine were administered free of charge to nearly 6% of the workers at the two exchanges. The number of vaccinated persons who were actually susceptible was not known.
Twenty-three complications occurred in 21 patients (Table 1). Fifteen (31%) of the 48 ill men reported epididymo-orchitis that lasted an average of 9 days (range: 2-21 days). One of two cases of pancreatitis and one case of aseptic meningitis occurred in men with epididymo-orchitis. One case each of oophoritis and arthritis was reported. Three women with mumps were pregnant; one developed premature labor that was subsequently arrested.
Nine (11%) of the 82 patients for whom data are available required hospitalization for a total of 41 days (range: 1-9 days; mean: 5 days) (Table 1). Epididymo-orchitis was responsible for four of nine hospital admissions.
Direct costs associated with health-care visits, medications, and hospitalizations for mumps were $56,406. Seventy-eight employees for whom data were available missed a total of 538 days of work (median: 7 days). The average cost per case was $1473 (Table 2). Reported by: M Ahrens, Highland Park Hospital; E Gary, W Martin, Immunization Program, D Marder, MD, LR Murray, MD, Chicago Dept of Health; K McMahon, C Jennings, R March, Immunization Program, BJ Francis, MD, State Epidemiologist, Illinois Dept of Public Health. Div of Immunization, Center for Prevention Svcs, CDC.
Editorial Note: Since licensure of live-virus mumps vaccine in 1967, the United States has made great strides in the control of mumps. Reported cases of mumps declined to a record low of 2982 in 1985 (1.2 cases/100,000 population), a 98% decrease from the 152,000 reported in 1968, the year mumps became a nationally notifiable disease. In 1986, however, the number of reported cases more than doubled (7790 mumps cases; 2.8 cases/100,000), a trend that continued through 1987, when the total was almost 12,900 cases. Through the first 30 weeks of 1988, 3166 cases have been reported, a 67% decrease from the same period in 1987.
Recent outbreaks have occurred in high schools and on college campuses, reflecting a change in the epidemiology of mumps and a shift in risk from elementary school-aged children to adolescents and young adults (1-4). During 1986-1987, 183 cases of clinically diagnosed mumps were reported from outbreaks at 10 Illinois colleges and universities (1,5). The increase in mumps cases in adolescents and young adults is particularly important in view of the more severe illness, higher frequency of complications, and greater costs associated with mumps in these age groups than in younger persons (4-8).
The types and rates of complications found during this investigation were similar to those found in other studies. For example, epididymo-orchitis affects 10%-38% of postpubertal males with mumps (6). The incidence of laboratory-verified aseptic meningitis increases with age and affects an estimated 0.6% of mumps cases in persons greater than or equal to20 years of age (9). Clinically symptomatic meningitis, characterized by headache and neck stiffness, is considerably more common. Mumps illness during the first trimester of pregnancy has been associated with an increased rate of spontaneous abortion possibly because of its effect on hormonal function of the placenta (10).
Benefit-cost analyses have shown that $7-$14 are saved for every dollar spent on mumps prevention (11,12). In the futures exchanges outbreak, the nearly $1500 cost for each mumps case contrasted dramatically with the cost of mumps vaccine, $4.47/dose in the public sector and $8.80/dose in the private sector in Chicago.
The age-specific changes in mumps epidemiology observed since vaccine licensure are similar to those noted for measles and rubella and reflect a vaccination policy oriented toward preschool and elementary school children. Although mumps vaccine was licensed in December 1967, it was less widely distributed than measles and rubella vaccines because of its relative expense** and its lower public health priority. Mumps vaccine was not recommended for universal use in children greater than or equal to12 months of age until 1977. Consequently, during 1967-1977, when mumps vaccine was used less prevalently, children may have had less exposure to mumps virus and no opportunity to receive mumps vaccine. As a result, a cohort of unvaccinated young adults may have remained susceptible as they entered the work force.
Direct evidence from field evaluations of vaccine efficacy and indirect evidence from vaccine use suggest that the failure to vaccinate susceptible persons, rather than vaccine failure or waning immunity, led to this outbreak (3,4). Most cases at the futures exchanges were reported in unvaccinated young adults, most of whom had been born and educated in Illinois, a state that until recently lacked a mumps immunization school law.
The effectiveness of school immunization laws in reducing the incidence of mumps has been consistently demonstrated (2,4,13). Illinois adopted comprehensive legislation in 1987 requiring mumps immunization for children enrolling in kindergarten through grade 12. Such legislation is unlikely to markedly affect the current cohort of susceptible older adolescents and young adults but will probably reduce the number of mumps cases among school attendees and among future cohorts of young adults.
Closed environments such as the trading floors of the Chicago futures exchanges facilitate contact with respiratory secretions and person-to-person transmission of mumps. A peak in the number of mumps cases corresponded to the surge in futures trading activity that preceded the October 19, 1987, market decline (Figure 1). Anecdotal information from interviews with patients suggests that the intense activity at the futures exchanges may have encouraged some employees with mumps to work despite their illness, thus possibly exposing susceptible co-workers to mumps. Furthermore, the peak infectiousness of mumps occurs during the 48 hours before the onset of overt clinical illness (14). Outbreaks of mumps in the prevaccine era characteristically occurred in closed populations such as prisons, orphanages, and among classes of military recruits (15). Whether outbreaks similar to the Chicago one will occur in other workplace settings will depend on the mumps susceptibility of the work force and the nature of the workplace setting.
The outbreak among the Chicago futures exchanges was costly and could have been averted. It should alert both employers and the health-care community to the existence of mumps in adults and should remind persons of the need to have documented immunity to mumps. Furthermore, employers should report promptly to public health authorities cases of suspected mumps among employees. Current recommendations for measles vaccination of adults assume that most persons born before 1957 were likely to have been naturally infected and thus generally do not require routine measles immunization (16). Based on the pattern of gradual introduction of mumps vaccine into use since 1967 and the preponderance of adult mumps cases in persons less than 30 years of age, it may be both useful and practical to follow a similar guideline as that used for measles as a means of preventing other mumps outbreaks in adult populations.
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