Imported Cases of Malaria — Puerto Rico, July–October 2015

Emilio Dirlikov, PhD1,2; Carmen Rodríguez, MS2; Shirley Morales, MPH3; Laura Castro Martínez, MPH2; Juan B. Mendez, MPH2; Anibal Cruz Sanchez, MPH2; Jesús Hernández Burgos, MPH2; Zobeida Santiago, MPH2; Rosa Ivette Cuevas-Ruis2; Sheila Adorno Camacho2; Enid Román Mercado2; Jessica Falcón Guzmán2,4; Kyle Ryff, MPH2; Carolina Luna-Pinto, MPH5; Paul M. Arguin, MD6; Stella M. Chenet, PhD6; Luciana Silva-Flannery, PhD6; Dragan Ljolje6; Julio Cadiz Velázquez, MD2; Dana Thomas, MD2,4; Brenda Rivera Garcia, DVM2 (View author affiliations)

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On July 16 2015, the Puerto Rico Department of Health (PRDH) was notified of a case of malaria, diagnosed by a hospital parasitology laboratory in a student who had traveled to Punta Cana, Dominican Republic, during late June for a school-organized graduation trip. Malaria is a mosquito-borne parasitic infection, characterized by fever, shaking chills, headaches, muscle pains, nausea, general malaise, and vomiting (1). Malaria can be clinically difficult to distinguish from other acute febrile illnesses, and a definitive diagnosis requires demonstration of malaria parasites using microscopy or molecular diagnostic tests. The student’s initial diagnosis on July 10 was suspected dengue virus infection. Puerto Rico eliminated local malaria transmission during the mid-1950s (2); however, reintroduction remains a risk because of the presence of a competent vector (Anopheles albimanus) and ease of travel to areas where the disease is endemic, including Hispaniola, the island shared by the Dominican Republic and Haiti, and the only island in the Caribbean with endemic malaria (3). During 2014, the Dominican Republic reported 496 confirmed malaria cases and four associated deaths; Haiti reported 17,662 confirmed cases and nine deaths (4). During 2000–2014, Puerto Rico reported a total of 35 imported malaria cases (range = 0–7 per year); three cases were imported from Hispaniola. During June–August 2015, eight confirmed malaria cases among travelers to the Dominican Republic were reported to CDC’s National Malaria Surveillance System (CDC, unpublished data, 2015).

After the student’s diagnosis of malaria, an epidemiologic investigation was undertaken by PRDH to identify additional cases among the 90 school trip participants. A suspected malaria case was defined as the occurrence of any symptoms consistent with malaria (i.e., fever, shaking chills, headaches, muscle pains, nausea, general malaise, and vomiting) occurring in a school trip participant ≥9 days after travel to the Dominican Republic. During interviews with participants, investigators learned that a second Puerto Rico school group (n = 44) had visited the same resort during the same time; thus, the investigation was expanded from 90 to 134 participants. To help find other suspected cases, PRDH released a health alert notice on July 17 to all health care providers in Puerto Rico; public health counterparts in the Dominican Republic were also informed.

Seven suspected cases were identified among school trip participants, and during July 16–August 21, health care providers in Puerto Rico sent 102 additional patient specimens to PRDH for evaluation by smear microscopy. Among the 109 total patient samples, 27 (25%) met the suspected case definition and were sent to CDC for testing by photo-induced electron transfer fluorogenic real-time polymerase chain reaction. Plasmodium falciparum malaria was diagnosed in five patients, including two from the first school group, two from the second school group, and one in an independent traveler from Puerto Rico (Table). Microsatellite loci evaluation indicated genetic similarity among isolates from the five patients as well as with previous malaria cases from Hispaniola. The five malaria patients were successfully treated. Two subsequent cases of P. falciparum malaria among self-organized travelers from Puerto Rico to Punta Cana were reported during September and October 2015.

This cluster of imported malaria cases highlights the importance of malaria surveillance in areas where the disease is not endemic to detect imported cases. Travelers should be informed of risks before visiting locations where malaria is endemic and take recommended precautions, including avoiding exposure to mosquitoes, using mosquito repellent, and taking recommended chemoprophylaxis ( Physician awareness of malaria symptoms and patient travel histories is critical for timely diagnosis and effective patient care. Febrile travelers from areas where malaria is endemic should be promptly evaluated by thin and thick smear microscopy for malaria infection, and public and private health institutions should maintain the ability to test for and report confirmed cases of malaria to public health authorities.


Bernard Christiansen, Grupo HIMA San Pablo; Puerto Rico Department of Health regional epidemiologists and Public Health Laboratory personnel.

Corresponding author: Emilio Dirlikov,, 734-635-0082.

1Epidemic Intelligence Service, Division of Scientific Education and Professional Development, CDC; 2Puerto Rico Department of Health; 3Cook County Department of Public Health, Illinois; 4Office of Public Health Preparedness and Response, CDC; 5CDC San Juan Quarantine Station; 6Malaria Branch, Division of Parasitic Diseases and Malaria, CDC.


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Return to your place in the textTABLE. Characteristics of patients with confirmed Plasmodium falciparum malaria who had traveled to the Dominican Republic — Puerto Rico, June–July, 2015
Patient no. Age (yrs) Sex Travel dates to Dominican Republic Travel type* Date of symptom onset Date first sought medical care Date of hospital admission Initial diagnosis suspected Date reported to PRDH
1 18 Male June 22–June 26 School trip 1 July 10 July 14 July 15 Dengue July 16
2 17 Female June 22–June 26 School trip 1 July 9 July 13 July 15 Dengue July 17
3 18 Male June 22–June 26 School trip 2 July 10 July 14 July 14 Viral syndrome July 20
4 47 Male June 22–June 27 Self-organized July 8 July 13 July 13 Dengue July 21
5 17 Female June 22–June 26 School trip 2 July 11 July 13 July 14 Viral illness July 20

Abbreviation: PRDH = Puerto Rico Department of Health.
* Epidemiologic investigation revealed cases resulting from two overlapping school trips to the same hotel in the Dominican Republic. An independent traveler staying at a different hotel in the region was also identified.

Suggested citation for this article: Dirlikov E, Rodríguez C, Morales S, et al. Notes from the Field. Imported Cases of Malaria — Puerto Rico, July–October 2015. MMWR Morb Mortal Wkly Rep 2016;65:326–327. DOI:

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