Malaria in the United States

Abstract & Commentary

By Stan Deresinski, MD, FACP, Clinical Professor of Medicine, Stanford, Associate Chief of Infectious Diseases, Santa Clara Valley Medical Center, is Editor for Infectious Disease Alert.

Synopsis: Four of the 1324 patients with malaria diagnosed in the United States and its territories in 2004, and reported to the CDC, died. Malaria was diagnosed in 30 pregnant women, and there were 3 cases of congenital malaria.

Source: Skarbinski J, et al. Malaria Surveillance—United States, 2004. MMWR Surveill Summ. 2006;55:23-37.

The CDC received reports of 1324 patients with malaria in the United States and its territories diagnosed in 2004; 4 patients died. This represented a 3.6% increase in cases from the previous year. US civilians accounted for 58.5% of cases. Of the 80.2% of cases in which species identification was accomplished, 49.5% were due to P. falciparum, 23.8% to P. vivax, 3.6% to P. malariae, and 2.0% to P. ovale; 1.3% of cases were due to mixed species infection.

Of the 4 autochthonous cases, one was laboratory-acquired and 3 were congenital. Of the remaining non-autochthonous cases, 68.0% were acquired in Africa, 14.5% in Asia, and 14.5% in Central and South America. Three US jurisdictions accounted for 35% of cases: the New York City Health Department reported 16.2% of cases, California 9.8%, and Texas 9.3%. Thirty cases of malaria occurred in pregnant women; only 10% took chemoprophylaxis. Four patients died.

Symptoms began < 1 month after arrival in the United States in 80.9% of P. falciparum infections and 43.0% of P. vivax infections. Of the patients for whom the information was available, 65.1% had taken no chemoprophylaxis, while 10.4% took inappropriate chemoprophylaxis. Of the 50 cases of P. vivax and 5 of P. ovale that occurred despite a history of having received appropriate chemoprophylaxis, 45.5% were consistent with relapsing infection occurring > 45 days after arrival in the United States. Nineteen cases were indeterminate due to lack of information. Only 11 cases, all caused by P. vivax, occurred < 45 days after arrival in the United States, consistent with chemoprophylaxis failure, but only 4 of these reported compliance with their regimen. Fifty-eight cases of P. falciparum infection occurred in individuals given appropriate chemoprophylaxis, but only 13 reported compliance.

Commentary

The major reason that cases of malaria continue to be seen in the United States is a lack of compliance with appropriate chemoprophylaxis during travel in endemic areas. A significant part of this problem is represented by travelers visiting family and friends, a group that comprised 52.6% of the patients with malaria. This is a group that unfortunately often eschews malaria prophylaxis.

There were 30 cases of malaria in pregnant women, and only 10% of these had taken chemoprophylaxis. The morbidity of malaria is increased in pregnancy and may, of course, affect the fetus, in addition to the mother. In general, pregnant women should avoid travel to malaria endemic regions. If they, nonetheless, elect to travel, in addition to taking measures to prevent mosquito bites, they should take chloroquine or mefloquine, depending upon the presence or absence of chloroquine resistance in the area visited. Atovaquone/proguanil, doxycycline, and primaquine should not be used. Febrile illness in neonates and infants born to mothers with a history of travel or emigration from a malaria endemic region, a history of malaria, or of illness compatible with malaria, should prompt examination of a peripheral blood smear.

Clinicians must remain alert to the diagnosis of malaria. In patients with a positive smear who have traveled to an area with chloroquine-resistant P. falciparum, treatment should be promptly initiated that is effective against these strains, even if the species cannot be immediately determined.