Epidemiologic Notes and Reports Measles Transmitted in a Medical Office Building -- New Mexico, 1986

On January 11, 1986, the Office of Epidemiology of the New Mexico Health and Environment Department received a report from a Santa Fe pediatrician of three suspected measles cases among patients in his group's practice. An active surveillance system was established, and over the ensuing 2 weeks, 24 patients meeting the standard Centers for Disease Control (CDC) clinical case definition for measles (1) were identified in New Mexico (Figure 2). These 24 patients had dates of onset ranging from January 4, 1986, to January 25, 1986. Three of the cases were excluded from analysis because of probable exposure outside the United States.

The patients with outbreak-related disease ranged from 5 months to 59 years of age (median 13.7 months). Seventeen cases occurred in patients who were 16 months old; one occurred in a 19-year-old patient who had been vaccinated; and one occurred in a patient who was born before 1957*. Nineteen cases were not preventable by CDC criteria (1). The two preventable cases were both in unvaccinated 16-month-old patients.

Nine of the 21 patients with outbreak-related disease had a known common exposure. Eight were seen in one pediatric practice between 8:30 a.m. and 2:00 p.m. on December 26, 1985. One was seen at 1:40 p.m. on the same day in an adjoining family practice clinic that is connected to the pediatric clinic by two hallways; these two clinics share a bathroom and laboratory. These nine patients ranged in age from 5 to 15 months. Seven of these nine cases were serologically confirmed. All nine patients developed a rash 13 to 17 days after their December 26 clinic visit (median = 14 days).

Eighty-four patients were seen in the pediatric clinic on December 26, 1985, and 34 patients were seen in the adjoining family practice clinic. Attack rates were 8/84 (10%) for the pediatric patients, 1/34 (3%) for the family practice patients, and 9/118 (8%) overall. However, there were no cases among the 85 patients over 15 months of age in either clinic. The attack rate among all patients aged 0 to 15 months was 9/33 (27%); among those aged 6 to 15 months the rate was 8/14 (57%). Arrival times of eight of the nine measles patients with a common exposure were clustered between 11:15 a.m. and 2:00 p.m. The one exception was a patient who arrived at about 8:30 a.m. but did not leave until about 10:30 a.m. Four of the six 6- to 15-month-old patients who did not contract measles arrived before 11:15 a.m. or after 2:00 p.m. From about 12:30 to 1:00 p.m. there were no patients in either waiting room, and the few patients remaining in the building during that time had no contact with each other.

Efforts to identify an index case were unsuccessful. Charts were reviewed on all 118 patients seen in the two clinics on December 26, and on 51 siblings of the pediatric patients and approximately 20 relatives of the family practice patients. Also, the parents of all patients who signed in at the pediatric practice between 9:30 a.m. and 1:00 p.m. were interviewed for information about rash-type illnesses in other household members.

The pediatric suite has a small (360 square foot), passive solar-heated waiting room with minimal air circulation. The child seen in the family practice suite who developed measles did not enter the pediatric waiting room, but probably did enter the bathroom which is 6 feet away from that waiting room. Examination rooms in both the pediatric and family practice areas are equipped with exhaust fans, but they generally are not used during the cold winter months. Reported by JL Sheline, MD, RL Lucer, DS Esquibel, RS Steece, MS, MS Stromei, HF Hull, MD, State Epidemiologist, New Mexico Health and Environment Dept; Div of Immunization, Center for Prevention Svcs, Div of Field Svcs, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: The proportion of measles cases acquired in medical settings increased from 0.7% during the period 1980-1982 (3) to 4.7% in 1985 (4). Medical settings may promote transmission by clustering in close quarters susceptible children who are too young to be vaccinated. No index case was identified in this outbreak. This raises the possibility that subclinical infection may have occurred in the index patient. Although acquisition of disease could be explained by close contact with an unidentified index case, airborne transmission almost certainly occurred in this outbreak (5). No patient who arrived before 12:30 p.m. was still in the office at 1:00 p.m. The index patient must, therefore, have arrived before lunch and departed before 1:00 p.m. The last patient to be infected arrived at 2:00 p.m., at least 60 minutes after departure of the hypothetical index case. Spread of virus between the pediatric and family practice areas probably occurred because of the open access between the two areas.

There have been at least two reports which give strong evidence for airborne transmission of the measles virus in physicians' offices (6,7). These reports identified several common factors: 50% or more of the cases were among children under 16 months of age; transmission occurred during cool autumn or winter months when there was low humidity; there was inadequate fresh air ventilation in the offices; and there was a maximum interval of 60 to 75 minutes between departure of the index case and infection of a later arriving patient. The outbreak in Santa Fe had similar features. Nine of the cases were in children 16 months of age; there was probably at least an hour between departure of the hypothetical index case and arrival of the last patient to be infected that day; and transmission occurred on a cool day in December (high temperature was 10 C (50 F)), in a small waiting room with virtually no air circulation. In addition, well children were not separated from sick children.

Transmission in Santa Fe County ceased after only two generations of infection. This is probably due to New Mexico's high measles immunization rate, which is 99.8% for the 14,000 children aged 12 months to 5 years in New Mexico's 327 licensed day-care centers and 98.6% for the 277,795 students in New Mexico's public schools.

References

1. CDC. Manual of procedures for national morbidity reporting and public health surveillance activities. Atlanta, Georgia: Public Health Service, 1985:9.46-9.48. 2 ACIP. Measles prevention. MMWR 1982;31:219.

2. Davis RM, Orenstein WA, Frank JA, et al. Transmission of measles in medical settings, 1980 through 1984. JAMA 1986;255:1295-8.

3. CDC. Measles--United States, 1985. MMWR 1986;35:366-70.

4. Langmuir AD. Changing concepts of airborne infection of acute contagious diseases: a reconsideration of classic epidemiologic theories. Ann New York Academy 1980;353:35-44.

5. Remington PL, Hall WN, Davis IH, Herald A, Gunn RA. Airborne transmission of measles in a physician's office. JAMA 1985;253:1574-7.

6. Bloch AB, Orenstein WA, Ewing WM, et al. Measles outbreak in a pediatric practice: airborne transmission in an office setting. Pediatrics 1985;75:676-83. *The Immunization Practices Advisory Committee has not recommended vaccination of persons born before 1957 because they "are likely to have been infected naturally and generally need not be considered susceptible" (2).

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