Problem/condition: Malaria in humans is caused by intraerythrocytic protozoa of the genus Plasmodium. These parasites are transmitted by the bite of an infective female Anopheles 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 2009 and summarizes trends during previous years.
Description of system: Malaria cases diagnosed by blood film, polymerase chain reaction or rapid diagnostic tests are mandated to be reported to local and state health departments by health-care providers or laboratory staff. 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), or direct CDC consults. Data from these reporting systems serve as the basis for this report.
Results: CDC received reports of 1,484 cases of malaria, including two transfusion-related cases, three possible congenital cases, one transplant case and four fatal cases, with an onset of symptoms in 2009 among persons in the United States. This number represents an increase of 14% from the 1,298 cases reported for 2008. Plasmodium falciparum, P. vivax, P. malariae, and P. ovale were identified in 46%, 11%, 2%, and 2% of cases, respectively. Thirteen patients were infected by two or more species. The infecting species was unreported or undetermined in 38% of cases. Among the 1,484 cases 1,478 were classified as imported. Among the 103 U.S. civilians for whom information on chemoprophylaxis use and travel area was known, only 34 (33%) reported that they had followed and adhered to a chemoprophylactic drug regimen recommended by CDC for the area to which they had traveled. Nineteen cases were reported in pregnant women, among whom none adhered to chemoprophylaxis. Almost 22% of the cases among pregnant women were treated with an inappropriate treatment drug regimen, of which 39% were among cases with either a P. vivax or P. ovale infection where primaquine was not taken. Among all the reasons for travel, travelers visiting friends and relatives (VFR) and missionaries were the groups with the lowest proportion of chemoprophylexis use.
Interpretation: A notable increase in the number of malaria cases was reported from 2008 to 2009; however, the number of cases in 2009 is consistent with the average number of cases reported during the preceding 4 years. 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. Furthermore, treatment of malaria, while appropriate for the majority of cases, was insufficient for a large number of P. vivax and P. ovale infections, putting patients at risk for relapsing malaria.
Public health actions: Decreasing the number of malaria cases in subsequent years will require conveying the importance of adhering to appropriate preventive measures for malaria specifically targeting travelers visiting friends and relatives, missionary, and pregnant populations. Clinicians require education on the need to encourage use of malaria prophylaxis and need further information on the appropriate diagnostic and treatment guidelines for malaria. Malaria prevention recommendations are available online (http://www.cdc.gov/malaria/travelers/ or http://wwwnc.cdc.gov/travel/yellowbook/2010/chapter-2/malaria.aspx#990). Malaria infections can be fatal if not diagnosed and treated promptly with antimalarial medications appropriate for the individual patient's age and medical history, the likely site of malaria acquisition, and previous use of antimalarial chemoprophylaxis. Clinicians should consult the CDC Guidelines for Treatment and contact the CDC's Malaria Hotline for case management advisement when needed. Malaria treatment recommendations can be obtained online (http://www.cdc.gov/malaria/diagnosis_treatment) or by calling the Malaria Hotline (770-488-7788).