Evaluation of malaria surveillance using retrospective, laboratory-based active case detection in four southwestern states, 1995.

The global resurgence of malaria has raised concerns of the possible reintroduction of indigenous transmission in the United States. The Centers for Disease Control and Prevention's National Malaria Surveillance System, using data supplied by state and local health departments (SLHDs), is maintained to detect local malaria transmission and monitor trends in imported cases. To determine the completeness of reporting of malaria cases to SLHDs, cases identified by local surveillance systems were compared with those identified through active case detection conducted at all laboratories that receive clinical specimens from 11 metropolitan areas in Arizona, California, New Mexico, and Texas. Of the 61 malaria cases identified through either local surveillance or active case detection, 43 (70%) were identified by SLHDs (range by metropolitan area = 50-100%) and 56 (92%) through active case detection. High percentages of cases were identified by SLHDs in New Mexico (80%) and San Diego County (88%), where laboratories are required to send positive blood smears to the SLHD laboratory for confirmation. Completeness of reporting, calculated using the Lincoln-Peterson Capture-Recapture technique, was 69% for SLHD surveillance systems and 89% for laboratory-based active case detection. The high percentage of cases identified by the 11 SLHDs suggests that the National Malaria Surveillance System provides trends that accurately reflect the epidemiology of malaria in the United States. Case identification may be improved by promoting confirmatory testing in SLHD laboratories and incorporating laboratory-based reporting into local surveillance systems.