Measles -- Puerto Rico

A measles outbreak in Puerto Rico began in July 1984 and continues into March 1985. From July 1, to October 31, 1984, 137 confirmed measles cases were identified by the Puerto Rico Department of Health and comprise the data for this report. Twenty-nine cases (21.2%) were serologically confirmed. In the preceding 6 months, one clinically confirmed case had been reported with rash onset in May. One hundred twenty patients (87.6%) lived in the Metropolitan Health Region, including 55 in each of two areas within the municipality of San Juan (Santurce and Rio Piedras) and 10 in the nearby town of Loiza. Many of the patients from the municipality of San Juan lived in public housing projects. The first two patients, both from Santurce, had onsets of rash on July 1 and July 3 (Figure 1). The source of their infections is unknown.

Of the 120 patients in the Metropolitan Health Region, 32 (26.7%) were under 1 year of age, 56 (46.7%) were under 16 months of age, and 111 (92.5%) were preschool-aged (under 5 years old) (Table 3). By contrast, 12 (70.6%) of the 17 patients outside the Metropolitan Health Region were school-aged or older (p = 4.6 X 10((-8))). The current recommended age for measles vaccination in Puerto Rico is 15 months.

The overall attack rate for the municipality of San Juan was 25 cases/100,000 population. Age-specific attack rates in the municipality were 769/100,000 for infants 6-11 months of age and 268/100,000 for children 1-4 years of age.*

Of the 137 total cases, 51 patients (37.2%) had diarrhea; 48 (35.0%) had vomiting; and 77 (56.2%) had one or both of these symptoms. The severity of these gastrointestinal symptoms, however, was unknown. Fifteen patients (10.9%) developed otitis media; six (4.4%) acquired pneumonia; and one (0.7%) developed meningitis. Twenty patients had at least one of these three complications, for a complication-to-case ratio of 14.6%. Twelve patients (8.8%) were hospitalized; the length of hospitalization ranged from 1 to 8 days (median 5 days). There were no measles-associated fatalities.

The probable setting of transmission was known for 62 (45.3%) of the cases: household/family contact--34 (54.8%); medical facility--14 (22.6%); neighborhood--13 (21.0%); school--1 (1.6%). There was no significant difference in the settings of transmission for the 14 patients under 1 year of age, compared to the 48 patients 12 months of age and older. Seventy-two cases (52.6%) were nonpreventable according to the CDC classification (1). Fifty-nine (81.9%) of these were nonpreventable because the patients were below the recommended age of vaccination. Twelve patients (16.7%) had histories of adequate vaccination, and one (1.4%) had a medical contraindication to measles vaccine.

Measures were taken to increase surveillance. Press releases were issued by the Puerto Rico Department of Health, and the outbreak was publicized by the news media on October 18. Information was distributed in neighborhoods throughout San Juan alerting people to the outbreak and recommending vaccination. Pediatricians were notified of the outbreak through a presentation at a pediatric conference on October 30 and by a letter sent out November 13. In early November, an active surveillance system involving public health clinics, private physicians, schools, licensed day-care centers, Head Start programs, and regional immunization nurses was developed.

Measles control activities of the various divisions within the Puerto Rico and municipal San Juan health departments were physically centralized in the commonwealth's Division of Maternal and Child Health. Case investigation was improved by providing epidemiologic training to investigators and by modifying the case investigation form. The few susceptible individuals identified at institutions (schools, day-care centers, Head Start programs) where patients with measles were enrolled were referred to public health clinics or private physicians for vaccination. Special vaccination clinics were established on November 13 at five different sites in the two major outbreak areas (Santurce and Rio Piedras) and were widely publicized. Two mobile vans provided measles vaccination in other areas.

Because of the large number of measles patients under 1 year of age, the recommended age of vaccination was lowered from 15 months to 6 months in the two major outbreak areas. Those from 6 to 11 months of age were to be given single-antigen measles vaccine and were scheduled to receive measles-mumps-rubella (MMR) vaccine at 15 months of age. Susceptible children 12 months of age or older were to be vaccinated with MMR. Those under 1 year of age who were direct contacts of a measles patient were to be given immune globulin. These recommendations have only been partially followed during the major portion of the outbreak. Reported by L Montalvo, MD, J Martinez-Gonzalez, MD, San Juan Dept of Health, T Robles, MD, I Carrion, MD, A Bonet, M Martinez, Metropolitan Health Region, M Sage, Immunization Program, JG Rigau-Perez, MD, Commonwealth Epidemiologist, Puerto Rico Dept of Health; Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Puerto Rico currently represents the focus of the greatest persistent measles activity in the United States and its territories. As of March 16, 1985, 293 cases have been reported as part of this outbreak. An additional imported case in a 2-year-old resident of San Juan with rash onset on December 2 was reported from Ohio. Until last year, the number of reported measles cases in Puerto Rico had declined from 2,021 in 1973 to 95 in 1983. The incidence rate over the same period fell from 70.4 cases/100,000 population to 2.9 cases/100,000 population (2).

A commonwealth school entry law, which was passed in 1974 and implemented in the 1975-1976 school year, required proof of measles vaccination before entering kindergarten or first grade. This was amended in September 1983 to require all persons under age 22 years to be immunized in order to attend day-care centers, primary, secondary, and postsecondary schools. The failure of this outbreak to spread significantly to the school-aged population suggests that the school laws have been successfully implemented.

In the current outbreak, 46.7% of patients were under 16 months of age, compared to 13.2% in the United States for the first 39 weeks of 1984 (3). From 1980 to 1983, there were 890 reported cases in Puerto Rico. Of 801 for whom age was known, 220 (27.5%) were under 1 year of age, and 513 (64%) were under 5 years of age. The age distribution of cases in Puerto Rico is more characteristic of that seen in developing countries than in the United States. It is a source of concern, since measles is a more serious illness in the youngest age groups (4).

Determinants of the age-specific incidence of measles include population density, mobility, patterns of human interaction, and child-rearing practices (5). Specifically, the following have been identified as factors contributing to onset at a young age: (1) overcrowding, (2) poor housing, (3) extended families, and (4) children being carried around by their mothers or siblings (6,7). Each of these elements was present in the outbreak areas in Puerto Rico. Additionally, working mothers in the affected public housing projects often leave children during the day in "unlicensed day-care centers" (i.e., neighbors' homes), where spread of measles among infants and young children has been implicated.

Like the age distribution, the frequency of diarrhea among measles patients in Puerto Rico is more characteristic of the disease in developing countries than in the United States. The severity of diarrhea in these patients, however, was unknown. Diarrhea associated with measles is particularly common in the tropics and may cause dehydration and death. The presence of diarrhea has been noted to correlate with the severity of measles (8).

The global case-fatality ratio in the developing world approaches 2% and has been reported to be as high as 25% in some countries (5,6). No deaths occurred in the present outbreak. Measles mortality may be lower in Puerto Rico than in developing countries because few risk factors for measles mortality are present. Of the four risk factors for measles mortality (5)--young age at onset, severe undernutrition, frequent and/or severe complications, and unavailable health care--only the first seems to be present in Puerto Rico.

The Puerto Rico outbreak illustrates the importance of the preschool population in disseminating measles in certain outbreaks. Although most susceptible school-aged children will be identified and vaccinated as implementation of immunization laws continues, ensuring age-appropriate immunization of the preschool-aged population remains a critical task in many areas. Possible approaches to reach preschool children 15 months of age and older include holding special preschool vaccination clinics, publicizing the importance of vaccination against measles in the community and in the local press, continuing enforcement of immunization laws for day-care centers and Head Start programs, and vaccinating susceptible children seen in medical facilities for other reasons. Measles in children under 16 months of age should decline as the incidence rate falls in other age groups by

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