Epidemiology of measles in the United States, 1997-2001.

Of the 540 measles cases (annual incidence, less than 1/million population) reported during 1997-2001 in the United States, 362 (67%) were associated with international importation: 196 imported cases, 138 cases epidemiologically linked to imported cases, and 28 cases associated with an imported measles virus genotype. The remaining 178 (33%) "unknown-source" cases were analyzed as potential evidence of endemic measles transmission. A total of 83 counties (2.6% of the 3140 US counties) in 27 states reported unknown-source cases; 49 counties reported only 1 unknown-source case, and the maximum reported by any county was 10. Nationally, unknown-source cases were reported in 103 of the 260 weeks. The largest unknown-source outbreak included 13 cases and lasted 5 weeks. The rarity of unknown-source cases, wide gaps in geographic and temporal distribution, and the short duration of the longest unknown-source outbreak indicate that endemic transmission of measles was not sustained in the United States during this period.

Lessons learned from establishing and evaluating indicators of the quality of measles surveillance in the United States, 1996-1998.

As part of a strategy to eliminate measles, 7 indicators were adopted in the United States in 1996 to ensure the quality of measles surveillance. This report summarizes the US experience with these indicators during 1996-1998. The indicators are compiled from data reported to the Centers for Disease Control and Prevention (CDC) during routine surveillance supplemented with information collected directly from states. Measles case investigations are generally thorough, and sufficient information is collected to control and monitor disease. A high proportion of measles cases are imported from other countries, suggesting that investigations are complete. For some states, the lag from disease onset to reporting is long, and the number of health department investigations of measleslike illnesses is low. Most of these investigations include laboratory testing of clinical specimens. Collection of measles virus specimens from cases for genetic analysis needs improvement. The CDC and health departments need to continue efforts directed at health care professionals to ensure the recognition, proper diagnostic workup, and reporting of measles.