ATLANTA - The annual number of reported measles cases in the Americas has decreased significantly since the region adopted the goal of measles elimination by 2000, but a resurgence of cases occurred in 1997.
Provisional data from January 1997 through February 1998 indicate that 88,485 suspected measles cases were reported from the region; 27,635 of which were confirmed - a substantial increase over the record low 2,109 confirmed cases in 1996, according to a recent report from the Centers for Disease Control and Prevention (CDC).
Canada (570 confirmed cases) and Brazil (26,348 confirmed cases) accounted for 97% of the confirmed cases.
The United States, Paraguay, Guadeloupe, Argentina, Chile, Venezuela and Costa Rica all reported more than 10 confirmed measles cases during 1997.
Each country in the region of the Americas, excluding the United States, the French Antilles and the Netherlands Antilles, conducted measles catch-up campaigns during 1987-1994. Since 1994, 26 (55%) of 47 countries and territories in the region have also conducted follow-up vaccination campaigns.
Of the 26,348 confirmed cases of measles reported from Brazil, 20,186 (77%) were reported from the state of São Paulo, which was the only Brazilian state not to conduct the follow-up measles campaign in 1995.
Patient age was reported for 19,322 con firmed measles cases from the São Paulo area; 9,938 (51%) of cases occurred in adults 20-29 years of age. However, the highest age-specific incidence rates were reported for infants younger than 1 year, young adults 20-29 years and children 1-4 years, the CDC said.
Twenty measles-related deaths were reported and 17 of those occurred in infants younger than 1 year.
Based on genomic sequencing of virus isolates conducted at the CDC, the virus circulating in São Paulo was similar to virus isolates recently obtained from Western Europe, suggesting the virus responsible for the outbreak may have been imported from Europe.
The virus spread to almost every other state in Brazil.
The CDC suggested that several factors may have contributed to the widespread measles transmission in São Paulo in 1997:
This outbreak demonstrates that the absence of measles virus circulation does not indicate the absence or risk for measles, according to the CDC. Major challenges for the region include: achieving and maintaining the highest population immunity levels possible in infants and children and supplemental activities to the existing strategies by targeting measles vaccination to high-risk adolescents and young adults; strengthening surveillance to detect groups susceptible to measles and possible sources of transmission established by measles importations; and, increasing worldwide efforts for control and elimination of the virus to decrease the quantity of measles virus exported to the Americas.
Canada reported 570 confirmed measles cases during 1997, more than 300 of which occurred among young adults in a university community in British Columbia. Most of the cases had been previously vaccinated with one dose of measles vaccine.
However, the virus spread from British Columbia to the neighboring providence of Alberta where 245 cases were reported, mostly among school-age children vaccinated with one dose of measles vaccine.
Genomic sequencing revealed the virus circulating in British Columbia was imported from Europe.
The United States reported the lowest number of measles cases (135) during 1997; this is less than half the previous record low of 309 reported in 1995. Fifty-seven (42%) of the cases were importations, primarily from Europe and Asia. Five cases confirmed as importations were reportedly from São Paulo. The largest U.S. outbreak during 1997 consisted of eight cases.
For more information:
- CDC. Progress toward elimination of measles from the Americas.MMWR 1998;10:189-93.
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