March 2, 2012 / 61(SS02);1-17
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 2010 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 1,691 reported cases of malaria, including 1,688 cases classified as imported, one transfusion-related case, and two cryptic cases, with an onset of symptoms in 2010 among persons in the United States. The total number of cases represents an increase of 14% from the 1,484 cases reported for 2009. Plasmodium falciparum, P. vivax, P. malariae, and P. ovale were identified in 58%, 19%, 2%, and 2% of cases, respectively. Thirteen patients were infected by two or more species. The infecting species was unreported or undetermined in 18% of cases. Among the 898 cases in U.S. civilians for whom information on chemoprophylaxis use and travel area was known, 45 (5%) reported that they had followed and adhered to a chemoprophylactic drug regimen recommended by CDC for the areas to which they had traveled. Forty-one cases were reported in pregnant women, among whom only two (5%) adhered to chemoprophylaxis. Among all reported cases, 176 (10%) were classified as severe infections, of which nine were fatal.
Interpretation: The number of cases reported in 2010 marked the largest number of cases reported since 1980. Despite the apparent progress in reducing the global burden of malaria, many areas remain malaria endemic and the use of appropriate prevention measures by travelers is still inadequate.
Public Health Actions: Travelers visiting friends and relatives (VFR) continue to be a difficult population to reach with effective malaria prevention strategies. Evidence-based prevention strategies that effectively target VFR travelers need to be developed and implemented to have a substantial impact on the numbers of imported malaria cases in the United States. A large number of pregnant travelers diagnosed with malaria did not take any chemoprophylaxis. Pregnant women traveling to areas in which malaria is endemic are at higher risk for severe malaria and must use appropriate malaria prevention strategies including chemoprophylaxis. Malaria prevention recommendations are available online (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. 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).
Two cases reported in 2010 were categorized as cryptic malaria because epidemiologic investigations did not identify a plausible mode of acquisition.
Case 1. A Ghanaian-American female aged 17 years, born in the United States, was hospitalized, treated, and recovered from a P. falciparum malaria infection in New York City in December 2010. The child's mother said that her daughter had not traveled outside the United States within the last 4 years, had not received blood transfusions, did not use IV drugs, did not have occupational exposure to blood products, and had no history of malaria. Because of unfavorable environmental conditions, local malaria transmission in the northeastern region of the United States during the winter season was an unlikely source of her infection. However, the New York City Department of Health and Mental Hygiene reviewed their vector-control data to determine whether the explanation of local transmission could be supported and found no data to support local transmission in the area where the patient lived. In the last attempt to discover the source of her infection, the public health authorities contacted the Ghana Embassy to verify her travel history. However, the embassy replied that information could not be disclosed to the public health authorities despite the circumstances. The origin of the infection remains undetermined.
Case 2. In November 2010, a woman aged 31 years sought treatment at a hospital emergency department for fever, severe headaches, nausea, vomiting, and malaise. She was admitted to the ICU for severe hyponatremia, thrombocytopenia, tachycardia, borderline splenomegaly, and epistaxis. Both the hospital and CDC confirmed a P. falciparum severe malaria infection with approximately 10% parasitemia. She was treated with oral quinine, clindamycin, and oral doxycycline, and recovered successfully. Probable routes of transmission were investigated. The patient stated that she had not traveled outside of the United States during the preceding 2 years and had no history of malaria. In 2008, she traveled to Nicaragua and stated that she had received malaria chemoprophylaxis at the time of her trip. She reported no history of blood transfusion or IV drug use. Mosquito trappings conducted around her home in Florida revealed no Plasmodium-infected mosquitoes, and no additional malaria cases in close contacts or persons residing in the area near her home. The origin of the infection remains undetermined.
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thanks to Krisztian Magori