Malaria in the United States
By Stan Deresinski, MD, FACP, FIDSA
Clinical Professor of Medicine, Stanford University
SYNOPSIS: The number of cases of imported malaria in the United States continues to increase, with most cases caused by Plasmodium falciparum and most of the infections acquired in Africa, particularly West Africa. Almost three-fourths of U.S. residents with malaria had failed to take chemoprophylaxis and the remaining one-fourth often had poor adherence with recommended medications.
SOURCE: Mace KE, Lucchi NW, Tan KR. Malaria surveillance — United States, 2017. MMWR Surveill Summ 2021;70:1-35.
This most recent Centers for Disease Control and Prevention (CDC) analysis of malaria diagnosed in the United States found that the 2,161 confirmed cases identified in 2017 was the highest number in 45 years. Plasmodium falciparum accounted for 1,523 (70.5%) of the total, while 216 (10.0%) were caused by Plasmodium vivax, 119 (5.5%) by Plasmodium ovale (119 [5.5%]), and 55 (2.6%) by Plasmodium malariae. In 22 cases (1.9%), the infection was caused by more than one species, while the species was not recorded in 226 cases (10.5%). Two of the cases were acquired congenitally, two were acquired by blood transfusion, and three were cryptic — i.e., no source could be identified in individuals without a history of travel.
Of the total number of cases, 1,819 (86.1%) were imported from Africa, with two-thirds of these from West Africa. Three-fourths of affected U.S. civilians who reported a reason for travel indicated they had been visiting friends and relatives. Only 28.4% of affected U.S. residents had taken chemoprophylaxis and, among these, adherence to the regimen was frequently poor, with 996 for whom the information was available either failing to adhere to the prescribed regimen or taking a regimen other than that recommended by CDC. Ten U.S. residents were among the 27 women who were pregnant and none of the 10 had taken chemoprophylaxis.
Symptoms of malaria began within 90 days after return to the United States in 94.8%. The malaria was classified as severe in 312 cases (14.4%) and seven of these patients died. Testing of 123 P. falciparum-positive samples failed to identify any with genetic polymorphisms associated with resistance to artemisinin. In contrast, such polymorphisms indicative of resistance to pyrimethamine were detected in 97.3%, to sulfadoxine in 69.4%, to chloroquine in 33.3%, to mefloquine in 2.7%, and to atovaquone in 2.7%.
The worldwide total number of cases of malaria in 2017 was approximately 219 million. Africa accounts for approximately 92% of global cases, and 99.7% of cases on that continent are caused by P. falciparum; 93% of all malaria deaths occur in Africa. The increased number of cases in the United States in 2017 represents a long-term continuation of an upward trend (see Figure 1), which, however, likely has been interrupted during the COVID-19 pandemic because of its effect on travel.
Figure 1: Number of Malaria Cases* Among U.S. Civilians, U.S. Military Personnel, and Non-U.S. Residents — United States, 1972-2017
R2 = square of the Pearson product moment correlation coefficient
* 2017: N = 2,161
Source: Mace KE, Lucchi NW, Tan KR. Malaria surveillance — United States, 2017. MMWR Surveill Summ 2021;70:1-35.
Lack of adequate (or any) prophylaxis continues to be the major cause of malaria in traveling U.S. residents. Efforts to confront this problem effectively must continue and intensify.
The number of cases of imported malaria in the United States continues to increase, with most cases caused by Plasmodium falciparum and most of the infections acquired in Africa, particularly West Africa. Almost three-fourths of U.S. residents with malaria had failed to take chemoprophylaxis and the remaining one-fourth often did not take recommended medications.
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