CDC: 2017 had highest number of malaria cases reported in US since 1971
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There were 2,161 confirmed cases of malaria in the United States in 2017 — the highest number since 1971, according to a report in MMWR.
“The majority of malaria infections in the United States occur among persons who have traveled to regions with ongoing malaria transmission,” wrote Kimberly E. Mace, PhD, and colleagues from the CDC’s Malaria Branch. “However, malaria is occasionally acquired by persons who have not traveled out of the country through exposure to infected blood products, congenital transmission, nosocomial exposure, or local mosquito-borne transmission.”
According to Mace and colleagues, in 2017 there was a relative increase of 4% in confirmed cases of malaria reported to the CDC from 2016, when there were 2,078 reported cases — the previous highest total since 1971. Cases in 1971 occurred predominately among military personnel who returned from deployment in Southeast Asia.
In 2017, a total of 1,290 (59.7%) cases of malaria were reported among U.S. civilians, 26 (1.2%) among U.S. military members, 516 (23.9%) among non-U.S. residents and 329 (15.2%) among people with unknown residential status.
It was determined that 2,112 cases (97.7%) were imported from countries where malaria is endemic. Only 42 cases had an incomplete travel history, which prevented the authors from classifying their origin.
According to the authors, the increase in current U.S. malaria cases coincides with an increasing trend of U.S. citizens taking international flights each year. Of the total number of cases reported in 2017, 84.2% originated in Africa, and the proportion of cases from West Africa increased from 51.1% in 2016 to 56.3%.
[Editor’s note: This story was updated to clarify that more malaria cases were reported in 2017 in the United States than in any other year since 1971.]
Perspective
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Those interested in malaria in the U.S. look forward to the annual release of the CDC summary of malaria cases reported in the country. The reports come out after a substantial delay, but nonetheless they are very informative. The report of cases from 2017 has just been released. What is new?
Malaria remains a significant problem in the U.S. The disease has not been transmitted locally since the 1950s, but cases are seen in Americans who return from international travel and in visitors from other countries. Indeed, in 2017 2,112 cases were diagnosed in the U.S., the largest number since the early 1970s, when high case numbers were driven by immigrants from southeast Asia at the conclusion of the Vietnam War. As in recent prior years, the large majority of cases in 2017 were caused by Plasmodium falciparum, the most lethal malaria parasite, and were contracted in Africa. The most common risk categories were those visiting friends or relatives of U.S. residents and refugees or immigrants for nonresidents. A total of 312 cases were classified as severe malaria, and seven cases had fatal outcomes; of those seven cases, five did not use malaria chemoprophylaxis and two had uncertain adherence.
Overall, updated CDC data for malaria showed a continued steady increase in reported cases in the U.S. in 2017. Obvious lessons are that use of chemoprophylaxis by high-risk travelers to malaria-endemic areas and consideration of the diagnosis of malaria in travelers returning from endemic areas with febrile illness are both essential. The incidence of malaria in the U.S. has probably decreased markedly with COVID-19-related travel restrictions in 2020 and 2021, but we can anticipate that, as the pandemic wanes and travel increases, we will again be seeing increasing numbers of cases of malaria in the U.S. in the coming years.
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