Measles -- United States, January 1-April 25, 2008

SB Redd; PK Kutty, MD; AA Parker, MSN, MPH; CW LeBaron, MD; AE Barskey, MPH; JF Seward, MBBS; JS Rota; PA Rota, PhD; L Lowe, PhD; WJ Bellini, PhD

Disclosures

Morbidity and Mortality Weekly Report. 2008;57(18):494-498. 

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Measles, a highly contagious acute viral disease, can result in serious complications and death. As a result of a successful U.S. vaccination program, measles elimination (i.e., interruption of endemic measles transmission) was declared in the United States in 2000.[1] The number of reported measles cases has declined from 763,094 in 1958 to fewer than 150 cases reported per year since 1997.[1] During 2000-2007,* a total of 29-116 measles cases (mean: 62, median: 56) were reported annually. However, during January 1-April 25, 2008, a total of 64 confirmed measles cases were preliminarily reported to CDC, the most reported by this date for any year since 2001. Of the 64 cases, 54 were associated with importation of measles from other countries into the United States, and 63 of the 64 patients were unvaccinated or had unknown or undocumented vaccination status. This report describes the 64 cases and provides guidance for preventing measles transmission and controlling outbreaks through vaccination, infection control, and rapid public health response. Because these cases resulted from importations and occurred almost exclusively in unvaccinated persons, the findings underscore the ongoing risk for measles among unvaccinated persons and the importance of maintaining high levels of vaccination.

Measles cases in the United States are reported by state health departments preliminarily to CDC, and confirmed cases are reported officially via the National Notifiable Disease Surveillance System, using standard case definitions and case classifications. Cases are considered importation associated if they are 1) acquired outside the United States (i.e., international importation) or 2) acquired inside the United States and either epidemiologically linked via a chain of transmission to an importation or accompanied by virologic evidence of importation (i.e., a chain of transmission from which a measles virus is identified that is not endemic in the United States). Other cases in the United States are classified as having an unknown source.

During January 1-April 25, 2008, a total of 64 preliminary confirmed measles cases were reported from the following areas: New York City (22 cases), Arizona (15), California (12), Michigan and Wisconsin (four each), Hawaii (three), and Illinois, New York state, Pennsylvania, and Virginia (one each) (Figure 1). Patients ranged in age from 5 months to 71 years; 14 patients were aged <12 months, 18 were aged 1-4 years, 11 were aged 5-19 years, 18 were aged 20-49 years, and three were aged ≥50 years, including one U.S. resident born before 1957.§

Number of reported measles cases* (N = 64) -- United States, January 1-April 25, 2008

Fourteen (22%) patients were hospitalized; no deaths were reported. Transmission occurred in both health-care and community settings. One of the 44 patients for whom transmission setting was known was an unvaccinated health-care worker who was infected in a hospital. Seventeen (39%) were infected while visiting a health-care facility, including a child aged 12 months who was exposed in a physician's office when receiving a routine dose of measles, mumps, and rubella (MMR) vaccine.

Fifty-four (84%) of the 64 measles cases were importation associated: 10 (16%) of the 64 were importations (five in visitors to the United States and five in U.S. residents traveling abroad) from Switzerland (three), Israel (three), Belgium (two), and India and Italy (one each); 29 (45%) cases were epidemiologically linked to importations; and 15 (23%) cases had virologic evidence of importation. The remaining 10 (16%) cases were from unknown sources; however, all occurred in communities with importation-associated cases. Specimens from 14 patients were genotyped at CDC, and four different genotypes were identified: three from Arizona (genotype D5), three from California (D5), five from New York City (one in a case epidemiologically linked to an imported case from Belgium and four in cases in communities where importations from Israel had occurred; all D4), two from Wisconsin (H1), and one from Michigan (D5).

Fifty-six of the 64 measles cases reported in 2008 have occurred in five outbreaks (defined as three or more cases linked in time or place). In New York City, an outbreak of 22 cases has been reported, including four importations and 18 other cases (10 importation associated). In Arizona, 15 cases have been reported; the index patient was an unvaccinated adult visitor from Switzerland. In San Diego, California, 11 cases have been reported, and an additional case spread to Hawaii; the index patient in the San Diego outbreak was an unvaccinated child who had traveled to Switzerland. In Michigan, four cases have been reported; the index patient was an unvaccinated youth aged 13 years with an unknown source of infection. In Wisconsin, four cases have been reported; the index patient was a person aged 37 years with unknown vaccination status who likely was exposed to a Chinese visitor with measles-compatible illness.

Sixty-three of the 64 patients were unvaccinated or had unknown or undocumented vaccination status, and one patient had documentation of receiving 2 doses of MMR vaccine. None of the five patients who were visitors to the United States had been vaccinated. Among the 59 patients who were U.S. residents, 13 were aged <12 months and too young to be vaccinated routinely, seven were children aged 12-15 months and had not yet received vaccination, 21 were children aged 16 months-19 years, including 14 (67%) who claimed exemptions because of religious or personal beliefs ( Table 1 ). Among the 18 patients aged ≥20 years, 14 had unknown or undocumented vaccination status, two had claimed exemptions and acquired measles in Europe, one had evidence of immunity because of birth before 1957, and one had documentation of receiving 2 doses of MMR vaccine.

Of the five U.S. residents with measles who were vaccine eligible and had traveled abroad, all were unvaccinated. One was a child aged 15 months who was not vaccinated before travel, and two were adults who were unvaccinated because of personal belief exemptions. For two adults, the reason for not being vaccinated was unknown.

*Based on MMWR surveillance summaries (2000-2006) and CDC unpublished provisional data as of December 31, 2007.

Measles clinical case definition: an illness characterized by a generalized maculopapular rash, a temperature of ≥101°F (≥38.3°C) and cough, coryza, or conjunctivitis. A case is considered confirmed if it is laboratory confirmed (using serologic or virologic methods) or if it meets the clinical case definition and is epidemiologically linked to a confirmed case.

§The other two cases in persons aged ≥50 years occurred in a U.S. resident aged 50 years and a visitor from Switzerland aged 71 years.

Two adults in the Arizona outbreak reported receipt of 1 and 2 vaccine doses, respectively, but lacked documentation.

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