Problem/condition: Malaria in humans is caused by intraerythrocytic protozoa of the genus Plasmodium (i.e., P. falciparum, P. vivax, P. ovale, and P. malariae). These parasites are transmitted by the bite of an infective female Anopheles species mosquito. The majority of malaria infections in the United States occur among persons who have traveled to areas with ongoing malaria transmission. In the United States, cases can occur through exposure to infected blood products, congenital transmission, or local mosquitoborne transmission. Malaria surveillance is conducted to identify episodes of local transmission and to guide prevention recommendations for travelers.
Period covered: This report summarizes cases in persons with onset of illness in 2006 and summarizes trends during previous years.
Description of system: Malaria cases confirmed by blood film or polymerase chain reaction (PCR) are mandated to be reported to local and state health departments by health-care providers or laboratory staff members. Case investigations are conducted by local and state health departments, and reports are transmitted to CDC through the National Malaria Surveillance System (NMSS), National Notifiable Diseases Surveillance System (NNDSS), and direct CDC consultations. Data from these reporting systems serve as the basis for this report.
Results: CDC received reports of 1,564 cases of malaria among persons in the United States with onset of symptoms in 2006, six of which were fatal. This is an increase of 2.4% from the 1,528 cases reported for 2005. P. falciparum, P. vivax, P. malariae, and P. ovale were identified in 39.2%, 17.6%, 2.9%, and 3.0% of cases, respectively. Ten patients (0.6%) were infected by two or more species. The infecting species was unreported or undetermined in 36.6% of cases. Compared with 2005, the largest increases in cases were from Asia (16.0%). Based on estimated volume of travel, the highest estimated relative case rates of malaria among travelers occurred among those returning from West Africa. Of 602 U.S. civilians who acquired malaria abroad and for whom chemoprophylaxis information was known, 405 (67.3%) reported that they had not followed a chemoprophylactic drug regimen recommended by CDC for the area to which they had traveled. Seventeen cases were reported in pregnant women, among whom only one reported taking chemoprophylaxis precautions. Six deaths were reported; five of the persons were infected with P. falciparum and one with P. malariae.
Interpretation: Despite the 2.4% increase in cases from 2005 to 2006, the numbers of malaria cases remained relatively stable during 2001--2006. No change was detected in the proportion of cases by species responsible for infection. U.S. civilians traveling to West Africa had the highest estimated relative case rates. In the majority of reported cases, U.S. civilians who acquired infection abroad had not adhered to a chemoprophylaxis regimen that was appropriate for the country in which they acquired malaria.
Public health actions: Additional investigations were conducted of the six fatal cases that occurred in the United States. Persons traveling to a malarious area should take one of the recommended chemoprophylaxis regimens appropriate for the region of travel and use personal protection measures to prevent mosquito bites. Any person who has been to a malarious area and who subsequently has a fever or influenza-like symptoms should seek medical care immediately and report their travel history to the clinician; investigation should always include blood-film tests for malaria, with results made available immediately. Malaria infections can be fatal if not diagnosed and treated promptly. CDC recommendations concerning malaria prevention are available at http://wwwn. cdc.gov/travel/contentdiseases.aspx#malaria or by calling the CDC Malaria Branch on weekdays (telephone: 770-488-7788; Monday--Friday, 8:00 A.M.--4:30 P.M. EST); during evenings, weekends, and holidays, call the CDC Director's Emergency Operations Center (telephone: 770-488-7100), and ask to page the person on call for the Malaria Branch. Recommendations concerning malaria treatment are available at http://www.cdc.gov/malaria/diagnosis_treatment/treatment.htm or by calling the CDC Malaria Hotline.