Malaria surveillance--United States, 2012.

Abstract

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 regions with ongoing malaria transmission. However, malaria is also occasionally acquired by persons who have not traveled out of the country, through exposure to infected blood products, congenital transmission, laboratory exposure, or local mosquitoborne transmission. Malaria surveillance in the United States 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 symptoms in 2012 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. For the first time, CDC conducted antimalarial drug resistance testing on blood samples submitted to CDC by health-care providers or local/state health departments. Data from these reporting systems serve as the basis for this report.

Results: CDC received 1,687 reported cases of malaria with an onset of symptoms in 2012 among persons in the United States, including 1,683 cases classified as imported, one laboratory-acquired case, one nosocomial case, and two cryptic cases. The total number of cases represents a 12% decrease from the 1,925 cases reported for 2011. Plasmodium falciparum, P. vivax, P. malariae, and P. ovale were identified in 58%, 17%, 3%, and 3% of cases, respectively. Twenty (1%) patients were infected by two species. The infecting species was unreported or undetermined in 17% of cases, a decrease of 6 percentage points from 2011. Polymerase chain reaction testing determined or corrected the species for 45 (43%) of the 104 samples submitted for drug resistance testing. Of the 909 patients who reported purpose of travel, 604 (66%) were visiting friends or relatives (VFR). Among the 983 cases in U.S. civilians for whom information on chemoprophylaxis use and travel region was known, 63 (6%) patients reported that they had followed and adhered to a chemoprophylaxis drug regimen recommended by CDC for the regions to which they had traveled. Thirty-two cases were reported in pregnant women, among whom only one adhered to chemoprophylaxis. Among all reported cases, 231 (14%) were classified as severe infections in 2012. Of these, six persons with malaria died in 2012. Beginning in 2012, there were 104 blood samples submitted to CDC that were tested for molecular markers associated with antimalarial drug resistance. Of the 65 P. falciparum-positive samples, 53 (82%) had genetic polymorphisms associated with pyrimethamine drug resistance, 61 (94%) with sulfadoxine resistance, 29 (45%) with chloroquine resistance, 1 (2%) with mefloquine drug resistance, 2 (3%) with atovaquone resistance, and none with artemisinin resistance.

Interpretation: Despite the 12% decline in the number of cases reported in 2012 compared with 2011, the overall trend in malaria cases has been increasing since 1973. Although progress has been made in reducing the global burden of malaria, the disease remains endemic in many regions, and the use of appropriate prevention measures by travelers is still inadequate.

Public health actions: Completion of data elements on the malaria case report form increased slightly in 2012 compared with 2011, but still remains unacceptably low. This incomplete reporting compromises efforts to examine trends in malaria cases and prevent infections. VFRs continue to be a difficult population to reach with effective malaria prevention strategies. Evidence-based prevention strategies that effectively target VFRs need to be developed and implemented to have a substantial impact on the numbers of imported malaria cases in the United States. Although more patients reported taking chemoprophylaxis to prevent malaria, the majority reported not taking it, and adherence was poor among those who did take chemoprophylaxis. Proper use of malaria chemoprophylaxis will prevent the majority of malaria illness and reduce the risk for severe disease (http://www.cdc.gov/malaria/travelers/drugs.html). Malaria infections can be fatal if not diagnosed and treated promptly with antimalarial medications appropriate for the patient's age and medical history, the likely country of malaria acquisition, and previous use of antimalarial chemoprophylaxis. Recent molecular laboratory advances have enabled CDC to identify and conduct molecular surveillance of antimalarial drug resistance (http://www.cdc.gov/malaria/features/ars.html). These advances will allow CDC to track, guide treatment, and manage drug resistant malaria parasites both domestically and globally. For this to be successful, specimens should be submitted for cases diagnosed in the United States and for ongoing specimen collection and testing globally. Clinicians should consult the CDC Guidelines for Treatment of Malaria and contact the CDC's Malaria Hotline for case management advice 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 or toll-free at 855-856-4713).