October 1999
ATLANTA - Analysis of epidemiologic data for 1998 suggests that measles is no longer indigenous to the United States. High measles vaccination coverage and strong surveillance remain critical to prevent imported measles cases from causing a resurgence in the United States, according to a report from the Centers for Disease Control and Prevention (CDC).
According to the CDC, 28% fewer measles cases were reported in 1998 than in 1997, revealing a record low number of cases. A preliminary total of 100 measles cases were confirmed and reported by state and local health departments in 1998, compared with 138 cases reported in 1997. In 1998, most U.S. residents with measles had been vaccinated with one or more doses of measles vaccine (53%). Eighty-six percent of international visitors with measles were unvaccinated.
The proportion of indigenous cases not associated with importation has declined from 85% in 1995, 72% in 1996, 41% in 1997, to 29% in 1998. Most of the reported cases in 1998 were associated with importation, including the short chains of indigenous transmission that were reported.
Of the 100 cases reported in 1998, 26 were internationally imported, or cases where case patients were infected outside the United States. Seventy-four of the cases were indigenous: 45 cases were importation-associated, while 29 were not importation-associated. The 45 importation-associated indigenous cases included 13 epidemiologically linked cases, or cases identified within a chain of transmissions caused by an internationally imported case. The other 32 cases were imported virus cases, or cases in which a chain of transmission from an imported measles virus was isolated, but a link to an internationally imported case was not identified.
During 1998, 28 states and the District of Columbia reported no confirmed measles cases, compared with 21 states in 1997. Eight states accounted for 82% of cases: 33 in Alaska, 11 in Arizona, 10 in Michigan, nine in California, eight in New Jersey, four in New York, four in Pennsylvania and three in Indiana. Two or fewer cases were reported in the remaining 14 states. Eight states reported indigenous measles cases not associated with importation.
![[bar]](/art/gradred.gif){kind=small}
The 26 internationally imported cases reported in 1998 represent the lowest number of imported cases since the recording of importation status began in 1983, according to the CDC. Imported cases from the Americas remained at very low levels, and imported cases from Europe and Asia declined compared with the previous four years. India, Japan, Kenya, Pakistan and Saudi Arabia each were the sources of two imported cases. Of 26 imported cases, 14 occurred among international visitors and 12 occurred among U.S. residents exposed to measles while traveling abroad.
All 32 imported virus cases occurred in an outbreak in Alaska, which began four weeks after an imported case of measles was diagnosed in a visitor from Japan. Measles virus isolated from cases in this outbreak was nearly identical to virus circulating in Japan. However, no virus was cultured from the imported case and no epidemiological link between the imported case and the outbreak was detected, according to CDC data.
In addition to the strain isolated from the Alaska outbreak, viral genomic sequencing of specimens from linked cases allowed genotype classification of measles virus strains from six chains of transmission epidemiologically linked to internationally imported cases. Virus strains isolated from cases in New York, Vermont, California, Massachusetts and Washington matched viral genotypes from Germany, Cyprus, Japan, China, and Croatia, respectively. Measles virus was isolated from the Indiana outbreak but genotype information was unavailable from Zimbabwe, the source country of the imported case.
Editor's note: There has been a recent outbreak of measles in Va. from an imported case. - P. Brunell, MD
For more information:
- CDC. Epidemiology of Measles - United States, 1998. MMWR 1999;48(34):749-53.
- CDC. Measles - United States, 1997. MMWR 1998;47:273-76.
- Rota JS, Rota PA, Redd SB, et al. Genetic analysis of measles viruses isolated in the United States, 1995-1996. J Infect Dis 1998;177:204-08.
- CDC. Measles, mumps and rubella - vaccine use and strategies for elimination of measles, rubella and congenital rubella syndrome and control of mumps: recommendations of the Advisory Committee on Immunization Practices. MMWR 1998;47(RR-8).
You can express your views on this
article, or other relevant themes, in the Infectious Diseases in
Children Specialty Forums.