Lessons from the 1996 Measles Epidemic
in Clark CountyKaren Steingart
infected several other high school students. One of these students then infected a high school cafeteria worker, who in turn infected three health care workers. Successive cases were confirmed in college students, health care workers, patients, and community residents. At least eight cases had occurred in the county before the index case; some of these persons had made multiple visits to health care providers before their diagnosis. The epidemic persisted through seven generations of cases before it terminated.
Only 301 cases of measles occurred in the United States in 1995, the lowest number in one year since measles reporting began in 1912. Only 17 cases occurred in Washington State and none in Clark County. This relative calm in measles activity was followed by a storm the next year, when Clark County experienced an epidemic affecting 33 persons. In this article we describe the epidemic and discuss consequent policy. The Index Case: On April 22, 1996, the Southwest Washington Health District (Clark, Skamania, and Klickitat counties) was notified of suspected measles in a 16-year-old tenth grader who the previous day arrived at a local hospital with vomiting and diarrhea. He had a temperature of 101 degree F respiratory symptoms, conjunctivitis, and photophobia. A rash appeared on his face that morning, he had spots in his mouth suggestive of measles. Although the initial laboratory test for measles was negative, a subsequent test was positive. The patient had received a single dose of measles vaccine at 15 months of age. The sidebar lists the clinical and laboratory criteria for diagnosing measles.
Epidemiologic Investigation
The source case was identified as a 17-year-old Japanese high school exchange student who was hospitalized in mid-March with a diagnosis of bronchitis and drug-related rash. She had arrived in Vancouver six days earlier. While in the hospital she infected an emergency department physician and another patient; she alsoEpidemic Management
Health district personnel collaborated with epidemiologists, immunization coordinators, and public information specialists from the state Department of Health (DOH). Two medical epidemiologists from the federal Centers for Disease Control and Prevention (CDC) were dispatched to assist with control efforts.Health district staff and volunteer physicians investigated more than 600 rash illnesses and conducted more than 200 clinical evaluations. The State Public Health Laboratory analyzed specimens and reported findings within 24 hours. With this quick turn-around we were able to direct control efforts to persons exposed to a confirmed case and administer measles-mumps-rubella (MMR) vaccine within 72 hours. The emphasis on laboratory diagnosis (rather than the clinical case definition) is a new way to manage a measles epidemic.
Vaccination was the mainstay of epidemic control. More than 30,000 doses of MMR were given in clinics at 20 county sites including primary and secondary schools, the community college, daycare centers, hospitals, private medical clinics, and worksites.
January 1, 1957 or documentation of physician-diagnosed measles or laboratory evidence of immunity). In mid-May, after two health care workers born before 1957 were diagnosed with measles, the definition of immunity was made more stringent by requiring one dose of vaccine or other evidence of measles immunity for health care workers born from 1948 to 1956.
Transmission in a Medical Facility
In late April, three cases of measles were reported in health care employees who worked in the same medical building but for three separate practices. All were likely infected by a single patient as the offices shared a common entrance and restrooms. To prevent further transmission, procedures were instituted to ensure that all health care workers were immune to measles and that suspect cases were promptly isolated. These measures included posting a sign describing the signs and symptoms of measles at the building entrance and stationing a nurse at the entry to facilitate the masking and isolation of patients with respiratory symptoms.Early in the epidemic, the health district faxed recommendations to health institutions and strongly advised that all health care workers, even those without patient contact, be immune to measles (defined by the Advisory Committee on Immunization Practices (ACIP) as having had two doses of live measles vaccine if born on or after
Thirteen measles cases (39%) were probably acquired in medical care settings. These cases included eight health care workers and five patients or visitors. These settings were one primary care practice, a multispecialty group, a health maintenance organization, a community hospital, and a home health agency associated with a hospital. Of the eight health care workers affected, one was a physician, two were medical or nursing assistants, three were clerks, and two worked in medical records. The median age of the cases among health care workers was 29.5 years with a range of 20 to 43 years. Two with documented vaccination had received their doses less than 14 days prior to rash onset. Three of the eight thought they had been vaccinated before the epidemic, but none could provide documentation. The patterns of measles virus transmission included patient to health care worker (four), patient to patient (two), health care worker to patient (three), health care worker to health care worker (two), and two undetermined.
Million-dollar Epidemic
The approximate cost of the epidemic was $1 million. This estimate includes overtime pay for health care workers and school officials, additional staff, printing and mailing costs, the value of government-supplied vaccine, direct medical costs, and missed work. Costs to the health district were estimated at $184,000.From March 14 through June 2, 1996, we identified 33 cases of measles (31 confirmed and two probable), for an attack rate of 11. 3 cases per 100,000 population (Figure 1). The mean age of the cases was 21 years, with a range of 5 months to 45 years. Nineteen cases (58%) occurred in persons aged 20 or older, including three in persons 40 to 49 years. Only 33% of cases had documented vaccinations; none had two doses. Age-specific incidence rates were highest for children under 5 and aged 15 to 19 (Table 1). Two persons were hospitalized, but no deaths occurred.
Following the epidemic, the local board of health required that all Clark County students from kindergarten through grade 12 be protected with two doses of measles vaccine beginning fall 1996. This strategy was supported by community physicians and school districts and made possible by the donation of free vaccine from the CDC.
Confirmed and probable cases of measles in Clark county; n=33 on June 14m 1996.4/30 -- Health district issues recommendations for measles immunity in health care workers.
5/13 -- College vaccination begins.
5/17 -- Hospital begins immunizing employees including those without direct patient contact.
Policy Questions
Why Clark County? Measles struck the county for three reasons: the lack of a two-dose measles vaccine policy for all school-aged children, measles-susceptible health care workers, and a chance international importation (a free airplane ride for the virus).1. The absence of a two-dose measles vaccine requirement for students in grades K-12. This outbreak was related to vaccine failure among school-aged children.
The age distribution of the cases reflected the measles vaccine policy in effect at the time, i.e., a second dose requirement at middle school entry. The highest incidence rates occurred in 15 to 19 year olds, particularly among high school juniors and seniors who entered middle school before the state second-dose requirement began in 1992. In response to the outbreak, the health district adopted a second-dose requirement for all K-12 students. International students must comply with the same standard. The ACIP is considering a recommendation that all school-aged children receive two doses of measles vaccine by 2001.2. Measles immunity for healthcare workers.
Health care workers are at greater risk of acquiring measles than are adults in the general population, and may transmit measles to already compromised patients. Such nosocomial transmission may disrupt care and lead to significant costs for emergency infection control measures.The lessons from this epidemic suggest that the 1989 ACIP recommendations to require two doses of measles vaccine at the time of employment for health care workers born after 1956 be strengthened. Health care institutions should adopt and implement policies requiring all employees born after 1956, not just newly hired employees or those providing direct patient care, to have documentation of two doses of live measles vaccine, and should consider requiring one dose of live measles vaccine or other proof of immunity for persons born before 1957.
3. International importations.
In the United States in 1996, the source case in six out-breaks (29% of the total reported) was traced to an international importation. Activities being accelerated worldwide to eliminate measles include improving vaccine coverage for infants, identifying and vaccinating hard-to-reach communities, and strengthening surveillance.Recommended Reading
Atkinson WL: Measles and healthcare workers infection control. Hosp Epidemiol 1994; 15:5-7.
Atkinson WL, Markowitz LE, Adams NC, Seastrom GR: Transmission of measles in medical settings, United States, 1985-89. Am J Med 1991; 91:320-324.
Centers for Disease Control and Prevention. Measles - U.S., 1995. MMWR 1995; 45:305-307.
Centers for Disease Control and Prevention: Progress toward global measles control and elimination, 1990-1996. MMWR 1997; 46:893-897.
Foulon G, Cottin JF, Matherson S, Perronne C, et al: Transmission and severity of measles acquired in medical settings. JAMA 1986; 256:1135-136.
Raad 11, Sherertz RJ, Rains CS, Cusick JL, et al: The importance of nosocomial transmission of measles. Infect Control Hosp Epidemiol 1989; 10:161-166.
Author
Karen Steingart, M.D., M,PH., is health officer for the Southwest Washington Health District.
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Created: 5/6/98 Updated: 7/15/99
