Malaria Surveillance — United States, 2010

Surveillance Summaries
March 2, 2012 / 61(SS02);1-17

Sonja Mali, MPH

S. Patrick Kachur, MD

Paul M. Arguin, MD

Division of Parasitic Diseases and Malaria, Center for Global Health

Corresponding author: Sonja Mali, MPH, Division of Parasitic Diseases and Malaria, Center for Global Health, 1600 Clifton Road, NE, MS A-06, Atlanta, GA 30333. Telephone: 404-718-4702; Fax: 404-718-4815; E-mail: smali@cdc.gov.

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 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).

Introduction

Malaria in humans is caused by infection with one or more of several species of Plasmodium (i.e., P. falciparum, P. vivax, P. ovale, P. malariae, and occasionally other Plasmodium species). The infection is transmitted by the bite of an infective female Anopheles mosquito. P. falciparum and P. vivax species cause the most infections worldwide. P. falciparum is the agent that most commonly causes severe and potentially fatal malaria (see Definitions). Worldwide, an estimated 216 million clinical cases and 655,000 deaths were reported in 2010, mostly in children aged <5 years living in sub-Saharan Africa (1). P. vivax and P. ovale have dormant liver stages, which can reactivate and cause malaria several months or years after the initial infection. P. malariae can result in long-lasting infections and if untreated can persist asymptomatically in the human host for years, even a lifetime (1). Approximately half of the world's population live in areas where malaria is transmitted (i.e., approximately 100 countries in parts of Africa, Asia, the Middle East, Eastern Europe, Central and South America, the Caribbean, and Oceania). Before the 1950s, malaria was endemic throughout the southeastern United States; an estimated 600,000 cases occurred in 1914 (2). During the late 1940s, a combination of improved housing and socioeconomic conditions, environmental management, vector-control efforts, and case management was successful at interrupting malaria transmission in the United States.* Since then, malaria case surveillance has been maintained to detect locally acquired cases that could indicate instances of local transmission and to monitor patterns of resistance to antimalarial drugs. Malaria vector mosquitoes are still present in the United States.
The majority of reported malaria cases diagnosed each year in the United States are imported from regions where malaria transmission is known to occur, although congenital infections and infections resulting from exposure to blood or blood products also are reported in the United States. In addition, occasionally, a case has been reported that might have been acquired through local mosquitoborne transmission (3).
State and local health departments and CDC investigate reported malaria cases in the United States, and CDC analyzes data from imported cases to detect trends in acquisition. This information is used to guide malaria prevention recommendations for international travelers.
The signs and symptoms of malaria illness are varied, but the majority of patients have fever. Other common symptoms include headache, back pain, chills, increased sweating, myalgia, nausea, vomiting, diarrhea, and cough. A diagnosis of malaria should always be considered for persons with these symptoms who have traveled to an area with known malaria transmission. Malaria also should be considered in the differential diagnosis of persons who have fever of unknown origin, regardless of their travel history. Untreated infections can rapidly progress to coma, renal failure, respiratory distress, and death. This report summarizes malaria cases reported to CDC among persons with onset of symptoms in 2010.