US Malaria cases rise, including 9 fatalies
June 1, 2012 6 minutes read
US Malaria cases rise, including 9 fatalies
By Lin H. Chen MD
Dr. Chen is Assistant Clinical Professor, Harvard Medical School and Director, Travel Medicine Center, Mt. Auburn Hospital, Cambridge, MA.
Dr. Chen has received research grants from the Centers for Disease Control and Prevention and Xcellerex.
Synopsis: Malaria cases in the US rose in 2010, including 9 fatalities. Preventive measures including chemoprophylaxis need to be emphasized especially during popular travel periods to malaria-endemic countries.
Source: Centers for Disease Control and Preventio. Malaria surveillance – United States, 2010. MMWR Surveillance Summaries 2012; 61(2):1-17.
CDC received 1691 reports of malaria diagnosed in the United States in 2010, a 14% increase from 2009, and the highest number of cases since 1980 (n=1864). Among these cases, 1131 were US residents, 368 foreign residents, and 192 had unknown status. Ten percent were classified as severe malaria and 9 patients (8 men and one woman) died; 7% of women diagnosed with malaria were pregnant. One case of malaria was transmitted via transfusion, and the transmission of 2 cases remained unclear.
Overall, the majority of patients had their exposures in Africa (63%), followed by Asia (19%), the Americas (15%), and Oceania (0.4%). Within Africa, West Africa contributed the most cases (73%), with a particularly notable 72% increase of cases acquired in Ghana from 2009. Within Asia, South Asia was the most common region of exposure with 94% of cases, and India was associated with 81% of these. The cases acquired in India increased 57% from 2009. Meanwhile, the Caribbean contributed the most cases in the Americas (77%), and Haiti was the exposure country in 96%, which represented a 66% increase from 2009. Nigeria, Haiti, and Ghana were the leaders, followed by Sierra Leone and Liberia, Cotes d'Ivoire, and Cameroon.
US residents most frequently acquired malaria in Africa. While this was also true for foreign visitors, Asia contributed a higher proportion to the region of exposure in foreigners. A few areas reported the majority of malaria cases: New York City, Florida, California, New Jersey, Texas, and Maryland. The most commonly reported reason for travel for US residents was to visit friends and relatives [VFR - 54%], followed by missionary activities (7%) and business (6%). The highest proportion was in persons aged 18-64 years, and 15% were in children <18 years of age and 5% in persons >65 years of age.
The species identification improved from what was reported in 2009. Among 1388 cases that had the causative species identified, Plasmodium falciparum remained the most common species (71%), followed by P. vivax (23%). Where the species and the region of exposure were reported, P. falciparum caused 86% of infections acquired in Africa, 81% in the Americas, 9% in Asia, and 40% in Oceania. P. vivax caused 6% of infections from Africa, 16% from the Americas, 87% in Asia, and 60% in Oceania.
The timing of the US cases peaked in January and July among patients who reported travel to Africa, associated with the winter and summer breaks in the US. The cases to Asia peaked in August with a smaller peak in November. For cases with known dates of arrival in the US and onset of illness, 11% had symptom onset before arrival, and the remainder mostly occurred within 1 month of arrival (84% of P. falciparum and 59% of P. vivax cases).
Analysis of chemoprophylaxis used among the US residents showed that about 25% took chemoprophylaxis, but 16% of those who specified a drug had taken one that was not recommended by CDC for their destinations. Sixty percent had missed doses among those who took recommended medications. Among those who took recommended chemoprophylaxis and had species identified (n=120), P. vivax and P. ovale accounted for 18% (n=22) and 8% (n=10), respectively, and included 12 cases that were considered relapses, rather than primary chemoprophylaxis failure, since they occurred >45 days after arrival to the US. Only 2 patients reported adherence, and had traveled to Africa and India taking mefloquine and atovaquone/proguanil, respectively. Six of the patients considered to have relapses received primaquine for anti-relapse therapy.
Among the failures with P. falciparum (n=80), nearly all were acquired in Africa or Haiti. Those that adhered to chemoprophylaxis (n=19) included 14 that traveled to Africa while taking mefloquine (n=7), doxycycline (n=5), and atovaquone/proguanil (n=2); 3 took chloroquine (n=2) or doxycycline (n=1) for travel to Haiti. All patients diagnosed with P. malariae who reported adherence (n=3) had exposures in Africa. Two took mefloquine and one took atovaquone/proguanil for chemoprophylaxis.
Treatment in uncomplicated cases was appropriate in 87% but inappropriate in 13%. The inappropriate treatments included using the same drug as that utilized for chemoprophylaxis. Less than half of the P. vivax and P. ovale patients received primaquine for anti-relapse therapy.
Commentary
The increase in malaria cases in 2010 is of concern, including the significant increase in pregnant women. Most of the fatalities occurred in persons who did not take malaria chemoprophylaxis, or used non-recommended regimens obtained abroad. West Africa remains the high-risk region, and Nigeria, Ghana, Sierra Leone and Liberia, Cotes d'Ivoire, and Cameroon continued to top the list. A dramatic increase (66%) in the total number of infections acquired in Haiti, and the cases among humanitarian workers there, illustrated probable intensified transmission as well as increased travel volume.1 Business travel appears to have emerged in importance as a cause of malaria alongside missionary travel, and business travelers should be advised appropriately.
The increase in pregnant travelers diagnosed with malaria is also worrisome. Most (83%) appeared to be VFRs, and prevention messages should aim for communities with high proportions of VFR travelers. If travel to malaria-endemic regions is unavoidable during pregnancy, mefloquine and chloroquine are recommended for chemoprophylaxis depending on parasite resistance. Of note, the USFDA changed mefloquine to a pregnancy category B drug, from category C, in 2011, endorsing its safety during all trimesters of pregnancy.2 Similarly, the peak incidences of malaria cases suggest the need for malaria prevention messages to target the popular travel seasons of winter holiday and summer vacations.
For a number of years, the most commonly reported reason for travel in patients diagnosed with malaria has been VFR. The year 2010 was no exception. Nearly half the cases in those <18 years old were children of foreign-born parents, indicating a group with significant risk that should receive focused malaria prevention education.3
The same regions within the US continue to report the highest numbers of malaria cases. These areas correspond to the presence of high population concentrations including foreign-born persons, high levels of travel, and are near major airline hubs for international flights; 4 therefore physicians in those areas should be well-trained in recognizing malaria risk and in the appropriate diagnosis and treatment.
P. falciparum remained the leading malaria species in Africa while P. vivax predominates in Asia and Oceania. However, P. vivax should not be neglected in the consideration of febrile travelers returning from Africa since it causes 1/16 of all malaria cases.
This surveillance found that the majority of malaria cases occurred within 1 month of arrival, which concurs with earlier data. However, significant proportions of P. vivax and P. ovale occurred beyond 3 months after return (16% and 42%, respectively), including a case of P. ovale that occurred >1 year after return. (See table.) Therefore, the diagnosis should still be considered long after exposure.
Although a few cases of chemoprophylaxis failure occurred, the analysis showed that most of the malaria cases did not take appropriate recommended chemoprophylaxis or were not adherent. Unfortunately, these cases might have been prevented if the patients had adhered to chemoprophylaxis. Even more tragic were the fatal cases for which chemoprophylaxis was neglected, mostly for travel to high-risk countries in West Africa.
Malaria treatment also needs improvement. Although a high proportion received appropriate treatment, those treated with the same drug as they had taken for chemoprophylaxis potentially confront resistant parasites that could have devastating outcomes. For severe malaria, intravenous artesunate achieves better parasite clearance and fever resolution than other malaria treatment regimens.5, 6 Artesunate is available through CDC by contacting the Malaria Hotline: 1-770-488-7788, 1-855-856-4713, or 1-770-488-7100. The CDC Malaria website for treatment assistance is: www.cdc.gov/malaria.
References
- Agarwal A, et al. The increase of imported malaria acquired in Haiti among US travelers in 2010. Am J Trop Med Hyg 2012;86:9-10.
- CDC. New recommendations for mefloquine use during pregnancy. Available at: http://1.usa.gov/uVWNuF. [Accessed April 16, 2012.]
- Han P, et al. Health Challenges of Young Travelers Visiting Friends and Relatives Compared with those Traveling for Other Purposes. Pediatr Infect Dis J 2012; in press.
- CDC. Malaria surveillance – United States, 2009. MMWR 2011;60(SS-3).
- Sinclair D, et al. Artesunate versus quinine for treating severe malaria. Cochrane Database Syst Rev 2011;16:(3):CD005967.
- Kreeftmeijer-Vegter AR, et al. Treatment outcome of intravenous artesunate in patients with severe malaria in the Netherlands and Belgium. Malar J 2012; 31;11(1):102. [Epub ahead of print]
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