Malaria Surveillance — United States, 2017
Authors: Kimberly E. Mace, Naomi W. Lucchi, Kathrine R. Tan
Journal: MMWR Surveillance Summaries (2021)

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 species mosquito.The majority of malaria infections in the United States occur among persons who have traveled to regions with ongoing malaria transmission.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 mosquitoborne transmission.Malaria surveillance in the United States is conducted to provide information on its occurrence (e.g., temporal, geographic, and demographic), guide prevention and treatment recommendations for travelers and patients, and facilitate rapid transmission control measures if locally acquired cases are identified.Period Covered: This report summarizes confirmed malaria cases in persons with onset of illness in 2017 and trends in previous years. Description of System:Malaria cases diagnosed by blood film microscopy, polymerase chain reaction, or rapid diagnostic tests are reported to local and state health departments through electronic laboratory reports or by health care providers or laboratory staff members.Case investigations are conducted by local and state health departments, and reports are transmitted to CDC through the National Malaria Surveillance System (NMSS), the National Notifiable Diseases Surveillance System (NNDSS), or direct CDC consultations.CDC reference laboratories provide diagnostic assistance and conduct antimalarial drug resistance marker testing on blood samples submitted by health care providers or local or state health departments.This report summarizes data from the integration of all cases from NMSS and NNDSS, CDC reference laboratory reports, and CDC clinical consultations.Results: CDC received reports of 2,161 confirmed malaria cases with onset of symptoms in 2017, including two congenital cases, three cryptic cases, and two cases acquired through blood transfusion.The number of malaria cases diagnosed in the United States has been increasing since the mid-1970s; in 2017, the number of cases reported was the highest in 45 years, surpassing the previous peak of 2,078 confirmed cases reported in 2016.Of the cases in 2017, a total of 1,819 (86.1%) were imported cases that originated from Africa; 1,216 (66.9%) of these came from West Africa.The overall proportion of imported cases originating from West Africa was greater in 2017 (57.6%) than in 2016 (51.6%).Among all cases, P. falciparum accounted for the majority of infections (1,523 [70.5%]), followed by P. vivax (216 [10.0%]),P. ovale (119 [5.5%]), and P. malariae (55 [2.6%]).Infections by two or more species accounted for 22 cases (1.0%).The infecting species was not reported or was undetermined in 226 cases (10.5%).CDC provided diagnostic assistance for 9.5% of confirmed cases and tested 8.0% of specimens with P. falciparum infections for antimalarial resistance markers.Most patients (94.8%) had symptom onset <90 days after returning to the United States from a country with malaria transmission.Of the U.S. civilian patients who reported reason for travel, 73.1% were visiting friends and relatives.The proportion of U.S. residents with malaria who reported taking any chemoprophylaxis in 2017 (28.4%) was similar to that in 2016 (26.4%), and adherence was poor among those who took chemoprophylaxis.Among the 996 U.S. residents with malaria for whom information on chemoprophylaxis use and travel region were known, 93.3% did not adhere to or did not take a CDC-recommended chemoprophylaxis regimen.Among 805 women with malaria, 27 reported being pregnant.Of these, 10 pregnant women were U.S. residents, and none reported taking chemoprophylaxis to prevent malaria.A total of 26 (1.2%) malaria cases occurred among U.S. military personnel in 2017, fewer than in 2016 (41 [2.0%]).Among all reported cases in 2017, a total of 312 (14.4%) were classified as severe malaria illnesses, and seven persons died.In 2017, CDC analyzed 117 P. falciparum-positive and six P. falciparum mixed-species samples for antimalarial resistance markers (although certain loci were untestable in some samples); identification of genetic polymorphisms associated with resistance to pyrimethamine were found in 108 (97.3%), to sulfadoxine in 77 (69.4%), to chloroquine in 38 (33.3%), to mefloquine in three (2.7%), and to atovaquone in three (2.7%); no specimens tested contained a marker for artemisinin resistance.The data completeness of key variables (species, country of acquisition, and resident status) was lower in 2017 (74.4%) than in 2016 (79.4%).