Sources of variability of estimates of malaria case counts, active and reserve components, U.S. Armed Forces

Each January, the Medical Surveillance Monthly Report (MSMR) estimates numbers of malaria infections among U.S. service members using a surveillance case definition to identify "malaria cases". These cases include individuals with a hospital discharge diagnosis of malaria and those who were reported with malaria through military notifiable event reporting systems. This report compares the MSMR surveillance case definition with other proposed case definitions to demonstrate the degree to which estimates of numbers of malaria cases are dependent upon clinical settings, data sources and case-defining rules used to produce such estimates. For example, including outpatient diagnoses as malaria cases would more than double the 2010 case count. As compared with cases defined using other proposed case definitions, many more MSMR-defined cases had records of a specific Plasmodium species, a laboratory test for malaria and recent travel to a malaria-endemic country. Interpretations of the results of MSMR reports should consider how "cases" are defined.