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Current Trends Measles -- United States, 1987
In 1987, a provisional total of 3655 measles cases was reported to CDC, a 42% decrease from the 6282 cases reported in 1986 (1) (Figure 1). The 1987 incidence rate was 1.5 cases/100,000 population, compared with 2.7 cases/100,000 population in 1986.
Detailed information was provided to CDC's Division of Immunization, Center for Prevention Services, on 3652 cases. Of these, 3312 (90.7%) met the standard clinical case definition for measles,* and 1106 (30.3%) were serologically confirmed. The usual seasonal pattern was observed, with the peak number of cases occurring from February through May (weeks 4-24) (Figure 2).
Three fourths (2759) of the cases were reported from New York City (469 cases) and seven states: California (809), Texas (452), New Mexico (318), Illinois (213), Missouri (190), New Hampshire (162), and Wisconsin (146). Incidence rates were greater than 3.0/100,000 population in New York City (6.5) and eight states: New Mexico (21.5), New Hampshire (15.8), Montana (15.5), Delaware (5.1), Oregon (4.9), Vermont (4.8), Missouri (3.8), and Wisconsin (3.1). Forty-one states and 265 (8.4%) of the nation's 3138 counties reported measles cases, compared with 46 states and 347 (11.1%) counties in 1986.
There were 76 outbreaks (i.e., five or more epidemiologically related cases), which accounted for 3165 (86.7%) cases. Seven outbreaks with more than 100 cases each accounted for 1877 (51.4%) cases. Eighty-three cases (2.3%) were known to be imported from other countries. Of these, 44 were in U.S. citizens. An additional 88 (2.4%) cases were epidemiologically linked to imported cases within two generations of onset in the index patient.
In 1065 (29.2%) cases, the patients were less than 5 years of age (Table 1); 482 (13.2%) were less than 15 months of age (297 children less than 12 months of age and 185 children 12-14 months of age). The 15-19-year age group accounted for 28.7% of all cases. The incidence rate of measles decreased from 1986 to 1987 in all age groups. The highest incidence rates occurred in 0-4-year-olds and 15-19-year-olds.
Complications were reported in 445 (12.2%) cases. Otitis media was reported in 209 (5.7%) cases; diarrhea, in 159 (4.4%); pneumonia, in 91 (2.5%); and encephalitis, in five (0.1%). Two hundred eighty-four (7.8%) of the reported patients were hospitalized. Four measles-attributable deaths were reported (death-to-case ratio of 1.1 deaths per 1000 cases) (2,3).
Of the 2451 (67.1%) patients for whom setting of transmission was reported, 1296 (52.9%) acquired measles in primary or secondary schools; 153 (6.2%), in medical settings; 141 (5.8%), in colleges or universities; 72 (2.9%), in child day care; 503 (2.0%), at home; and 286 (11.7%), in a variety of other settings.
A total of 1734 (47.5%) patients had been vaccinated on or after the first birthday, including 609 (16.7%) who were vaccinated at 12-14 months of age. One hundred sixty-nine (4.6%) had a history of vaccination before the first birthday, and 1749 (47.9%) were unvaccinated. Of the 2101 school-aged children 5-19 years of age, 1506 (71.7%) had been adequately vaccinated, including 579 (27.6%) who were vaccinated at 12-14 months of age. In contrast, of the 1065 preschool-aged children 0-4 years of age, 153 (14.4%) had been adequately vaccinated, including 20 (1.9%) vaccinated at 12-14 months of age (Table 2).
Measles cases are classified as preventable or nonpreventable. A case is defined as preventable if it occurs in a person for whom vaccine is indicated by current recommendations (4,5). Of the 3652 cases, 1010 (27.7%) were classified as preventable (4) (Table 2). From 1986 to 1987, the absolute number and proportion of cases that were preventable through vaccination decreased in all age groups except those greater than or equal to25 years of age. The highest proportion of cases that were preventable through vaccination occurred in adults 25-29 years old and in children 16 months-4 years old. In contrast, fewer than one fifth of cases in school-aged children 5-19 years of age were preventable through vaccination. However, 40.1% of all preventable cases occurred in this age group.
A total of 2642 cases were classified as nonpreventable. Of these, 1718 (65.0%) were in persons who had been vaccinated on or after the first birthday; 526 (19.9%) were in children too young for routine vaccination (less than 16 months of age); 216 (8.2%) were in persons with medical contraindications or exemptions under state law; 126 (4.8%) were in persons older than the recommended age for vaccination (born before 1957); 45 (1.7%) were international importations in non-U.S. citizens; and 11 (0.4%) were in persons with a prior physician diagnosis of measles (Table 3). Reported by: Div of Immunization, Center for Prevention Svcs, CDC.
Editorial Note: The decrease in number of cases reported in 1987 reverses the trend of annual increases in measles incidence since the record-low year 1983, when 1497 cases were reported. The number of cases reported in 1987 represents a 99% reduction from the prevaccine era. Incidence rates in 1987 decreased from 1986 in all age groups; the largest decrease was in children less than 5 years of age. The overall decline observed in 1987 has continued into 1988; the provisional 1988 case count through week 27 is approximately 40% below the 1987 level. Reasons for the decline in measles cases may be multiple--secular trends, exhaustion of susceptibles in some areas from which large numbers of cases have previously been reported, or fewer importations in 1987.
As in previous years, almost one third of cases reported were classified as preventable, i.e., patients were eligible for vaccination but unvaccinated. Many of these cases occurred in preschool-aged children living in inner-city areas. Innovative strategies are needed to increase immunization levels in these populations.
Most cases reported in 1987, however, were classified as nonpreventable and occurred in school-aged children who had been vaccinated on or after the first birthday. Most of these cases probably result from primary vaccine failure, i.e., the failure to seroconvert following vaccination; there is little epidemiologic evidence to indicate that secondary vaccine failure or waning immunity is a major problem. The approximate primary measles vaccine failure rate of 5% (range 2%-10%) may provide enough susceptibles to sustain an outbreak among highly vaccinated populations (6) in some settings. Moreover, persons vaccinated at 12-14 months of age are at slightly higher risk for measles than are persons vaccinated at greater than or equal to15 months (7).
The four deaths reported in 1987 are the first measles-attributable deaths reported to the Division of Immunization since 1985. All deaths occurred in immunocompromised patients, including two children with AIDS. Since large measles outbreaks have occurred in areas with high prevalence of human immunodeficiency virus (HIV) infections and since HIV-infected persons appear to be at increased risk for serious complications (3), the Immunization Practices Advisory Committee (ACIP) recommends that asymptomatic HIV-infected children be vaccinated with measles, mumps, and rubella (MMR) vaccine and that consideration be given to vaccinating sympto matic HIV-infected children (8).
A group of expert consultants was recently convened by CDC to consider the problem of continuing measles transmission in the United States. The consultants felt that the goal of measles elimination should be pursued. They reviewed the two predominant patterns of measles: 1) measles in unvaccinated preschool-aged children--a failure to implement the current strategy, and 2) infections in adequately vaccinated school-aged children--a failure of the current strategy. These two patterns require different solutions. Increased efforts are needed to vaccinate preschool-aged children. Vaccination schedules may need to be modified in selected high-risk areas. Proposed changes include lowering the recommended age for routine vaccination and/or instituting a two-dose schedule. Aggressive revaccination strategies may also be necessary to control outbreaks among highly vaccinated school-aged populations. These recommendations are being evaluated by ACIP. In the meantime, efforts should continue to ensure that all susceptible persons are vaccinated and that appropriate surveillance and outbreak-control procedures are practiced.
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