Imported Measles with Subsequent Airborne Transmission in a Pediatrician's Office -- Michigan

An outbreak of seven cases of measles was reported in Muskegon County, Michigan; rash onsets occurred from November 14 through December 10, 1982. The outbreak began with an international importation in a 7-month-old baby who arrived in the United States from Korea on October 29 for adoption. She infected four other children in a pediatrician's office; two additional measles cases occurred subsequently in family members of these four children (Figure 1).

The index patient (Patient A) had onset of rash on November 14 and visited a pediatrician's office on November 16. She was in the office waiting room from 11 a.m. to noon and in a single examination room from noon to 12:30 p.m. After measles was diagnosed, the pediatrician reviewed the immunization records of all children known to be in the office at the same time and offered immune globulin (IG) to the three unimmunized children, all of whom were less than 15 months of age. Two received IG, while the third, a 6-month-old infant did not. No cases occurred among these children. However, cases did occur in patients not known to have been in the office at the same time as Patient A. One child who was subsequently infected arrived approximately 5 minutes before Patient A left the office but did not have face-to-face contact with her; the other three arrived in the office 60-75 minutes after Patient A left. Only one of these four children used the same examining room as Patient A, but all four shared the same waiting room. None of the children were in contact with any other persons who had rash illnesses. No other common activities or contacts with individuals or shared objects could be identified to account for these cases. The last-known measles cases in Muskegon County had been reported in February 1981.

The patients with secondary cases ranged in age from 4 months to 2H years; none had been immunized. Two of these children transmitted measles to family members--a 14-year-old, with a history of measles vaccination at 11 months and 5 years, and a 24-year-old, whose immunization status was unknown.

Of 29 children who were in the office when Patient A was present or who arrived within 90 minutes of her departure, 19 were 15 months of age or older, the recommended age for routine measles vaccination. Two of these children had not been vaccinated; both developed measles. None of the 17 vaccinated children developed measles. Of 10 children less than 15 months of age, all unvaccinated, two were infected, two received IG, and six remained well. Four of the six well patients were 6 months of age or less. Reported by B Davies, MD, M Galvin, MD, A Herald, MD, B Joseph, Nursing Staff, Muskegon County Health Dept, Muskegon; G Walsh, W Hall, MD, KR Wilcox, MD, State Epidemiologist, Michigan Dept of Public Health. Div of Field Svcs, Epidemiology Program Office; Hospital Infections Program, Center for Infectious Diseases; Surveillance, Investigations, and Research Br, Div of Immunization, Center for Prevention Services, CDC.

Editorial Note

Editorial Note: The index case in this outbreak was an international importation, a child who was too young to have received routine vaccination against measles. Transmission from this importation was limited because the immunity level in this physician's practice and the community was high. Protection afforded by measles vaccine was demonstrated by the lack of secondary cases in children who had been vaccinated. Record reviews in Muskegon County schools (enrollment approximately 10,000) showed that over 99% of students were immune to measles.

The outbreak appears to have been caused by airborne transmission in the pediatrician's office; none of the secondary cases were in children who had face-to-face contact with Patient A. Transmission probably occurred when droplet nuclei were aerosolized by the coughing child, remained suspended and were subsequently inhaled by the other children when they arrived; this phenomenon has been described in a medical office, an airport, and other settings (2-4). This outbreak indicates that transmission in medical offices can occur up to 75 minutes after an infectious patient has left the office. Survival of measles virus in droplet nuclei for over 2 hours has been demonstrated in laboratory studies (5). Although the exact mode of transmission in this instance cannot be proven, transmission via fomites seems less likely than airborne transmission because measles virus is believed to survive only for a short time on dry surfaces (6).

When patients with illnesses compatible with measles present for medical care, they should be cared for in a way that minimizes contact with other patients. Considering the high communicability of measles, it seems reasonable to keep such patients in respiratory isolation (7), to attend them promptly, and to consider postexposure prophylaxis for susceptible office contacts--staff as well as patients. Such prophylaxis should be administered to persons who had direct face-to-face contact with the infectious patient. Prophylaxis is not generally offered to persons who did not have face-to-face contact but were in the office with the patient or arrived after the patient departed. The risk of measles in the latter group is uncertain because data are not available to accurately determine the frequency of airborne transmission in medical offices. The fact that airborne transmission has only rarely been documented suggests that the risk is low and that, ordinarily, postexposure prophylaxis is unnecessary for such persons.

Measles vaccination may provide protection if given within 72 hours of exposure (8). Because there is no evidence of adverse reactions following vaccination of immune individuals, combined measles-mumps-rubella vaccine (MMR) should be used whenever a person is likely to be susceptible to more than one component. IG may prevent or modify measles if given within 6 days of exposure. IG may be especially indicated for susceptible close contacts of measles patients, particularly contacts under 1 year of age, for whom the risk of complications is highest. If IG is used, measles vaccine should be given about 3 months later if the child is at least 15 months of age.

As long as measles cases continue to occur or are imported into the United States, persons who visit physicians' offices and other medical settings may have some risk of exposure; infection may follow exposure to patients or health-care personnel (9). Ideally, both groups should be immune to measles to minimize this risk, especially for patients who are too young for routine vaccination or who cannot be vaccinated because of medical contraindications.

References

1. Amler RW, Bloch AB, Orenstein WA, Bart KJ, Turner PM, Hinman AR. Imported measles in the United States. JAMA 1982;248(17):2129-33.

2. Bloch AB. Measles in a private physician's office. Proceedings of the 16th Immunization Conference, May 18-21, 1981, Atlanta, CDC:59-63.

3. Langmuir AD. Changing concepts of airborne infection of acute contagious diseases: a reconsideration of classic epidemiologic theories. In: Airborne contagion. Kundsin RB, ed. New York: Annals of the New York Academy of Sciences 1980;353:35-44.

4. CDC. Interstate importation of measles following transmission in an airport--California, Washington, 1982. MMWR 1983;32:210,215-16.

5. DeJong JG, Winkler KC. Survival of measles virus in air. Nature 1964;201:1054-5.

6. Black FL. Measles. In: Viral infections of humans. Evans AS, ed. New York: Plenum Medical 1976:300.

7. Garner JS, Simmons BP. Guideline for isolation precautions in hospitals. Infect Control 1983;4:245-325.

8. Immunization Practices Advisory Committee. Measles prevention. MMWR 1982;31:217-24,229-31.

9. CDC. Measles in medical settings--United States. MMWR 1981;30:125-6.

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