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Imported Malaria and Use of Malaria Chemoprophylaxis by Travelers -- Kentucky, Maryland, and United States, 1993-1994

Malaria surveillance has been maintained in the United States since indigenous transmission was interrupted in the late 1940s. Most reported cases in this country are acquired during international travel or occur among persons who resided in malaria-endemic countries. During 1993-1994, the number of reported cases increased in Kentucky and Maryland. This report summarizes the investigations of these cases and compares findings with national data from 1993, which indicate many travelers who acquired malaria infection failed to take appropriate chemoprophylaxis.

Kentucky. During 1993-1994, a total of 16 confirmed cases of malaria (Table_1) were reported to the Kentucky Department for Public Health, twice the total reported during 1991-1992. Case report forms were reviewed, and additional clinical information was obtained through review of hospital medical records and by contacting patients, reporting physicians, or military health officers. Most infections were acquired in Africa (seven {44%}), followed by Central America (six {38%}) and Asia (three {19%}). Three of the six U.S. civilians with malaria reported using chemoprophylaxis during exposure; none of these patients had used a drug recommended by CDC. Of the three civilians who did not use prophylaxis, two were unaware of the need, and one was aware but did not use it.

Maryland. In Maryland, 83 cases of malaria were reported in 1994, a 46% increase over the 57 cases reported in 1993. CDC Malaria Case Surveillance Report forms, Maryland Confidential Morbidity Report forms, and laboratory reports were reviewed; local health departments were contacted for missing data. Of the 75 cases with known country of travel, 53 (64% of all cases) were acquired in Africa. Of the 37 U.S. civilians for whom data were available, 13 (35%) reported use of chemoprophylaxis during the period of probable exposure (Table_1). Of nine U.S. civilians for whom information about chemoprophylaxis was available, two (22%) had used a drug recommended by CDC. The adequacy of their dosing regimens was unknown.

United States. In 1993, state and territorial health departments reported 1275 cases of malaria to CDC (CDC, unpublished data, 1993), a 40% increase over the 910 cases reported in 1992 (1). The increase reflected cases among military personnel returning from Somalia and improved reporting of cases identified in New York City. Most malaria cases were acquired in Africa (58%), followed by Asia (20%) and Central America and the Caribbean (11%) (Table_1). Eight deaths were associated with infection with Plasmodium falciparum. Of the 482 U.S. civilians with imported malaria for whom information about use of chemoprophylaxis was available, 253 (52%) used chemoprophylaxis during the period of probable exposure. Of the 225 persons for whom information about drugs used were available, 109 (48%) used recommended drugs; 57 (52%) of these patients had infections consistent with relapse of P. vivax or P. ovale infection. Of the 34 nonrelapse-associated cases for which data about dosing regimen were available, 11 (32%) used recommended doses of mefloquine, and 23 (68%) were noncompliant. Five of the 11 persons who were compliant had P. falciparum infection. Serum levels of mefloquine were inadequate to provide protection from blood stage infection in four of these five cases for whom levels were measured (2). The remaining six persons who were compliant were diagnosed with P. malariae infection 1-2 months after completing their course of chemoprophylaxis. Overall, 84% of U.S. civilians with malaria reported that they had not used or had incorrectly used chemoprophylaxis.

Reported by: D Embry, Jefferson County Health Dept, Louisville; R Finger, MD, State Epidemiologist, Dept for Public Health, Kentucky Cabinet for Health Svcs. M Ryan, MD, C Kratt, MD, C Groves, J Moses, MD, E Porter, MD, E Israel, MD, D Dwyer, MD, State Epidemiologist, State of Maryland Dept of Health and Mental Hygiene. Malaria Section, Epidemiology Br, Div of Parasitic Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Malaria is preventable through effective chemoprophylactic regimens that are safe and well tolerated (3). The drug of choice for travel to most areas with chloroquine-resistant P. falciparum is mefloquine. In a previous survey of 139,000 European travelers to East Africa, the frequencies of adverse reactions to mefloquine and chloroquine were similar and included reports of dizziness in 7.6% and 5.3% of mefloquine and chloroquine users, respectively, and serious neuropsychiatric reactions (i.e., fatal, life-threatening, or disabling reactions or reactions that resulted in or prolonged a patient's stay in a hospital or lead to malignancy or congenital anomaly) in 0.009% and 0.007%, respectively (3).

The objectives of the national malaria surveillance system are to identify episodes of malaria transmission in the United States and to monitor trends in imported cases. Information collected about trends in imported cases of malaria and on the effectiveness of chemoprophylactic measures used by travelers assists in guiding prevention recommendations (4). The reasons for the increase in reported cases in Kentucky and Maryland are unknown but may include increased travel to malaria-endemic areas. In these two states and nationally, most persons who contracted malaria during travel to a malaria-endemic area failed to use appropriate chemoprophylaxis. Of those who did use chemoprophylaxis, fewer than half used an optimal drug or dosing regimen for preventing malaria. Similarly low rates of compliance with chemoprophylactic regimens (40%-50%) have been documented in surveys of travelers (5-7).

Failure of prophylaxis may occur for at least four reasons. First, travelers may not seek or follow advice or may receive inaccurate advice regarding antimalarial medication. Second, travelers may forget to use prophylaxis, may not completely understand chemoprophylactic advice, or may be advised by peers not to use chemoprophylaxis (7). Third, persons who visit friends or relatives living in areas with endemic malaria often are less likely than other tourists to obtain pretravel advice (8) or to use chemoprophylaxis (5,8) and are more likely to have malarial illnesses (9). Fourth, many physicians infrequently provide pretravel advice to patients and may not be aware of the current recommendations.

Prevention of malaria requires educating travelers about the health risks associated with travel and the need to obtain pretravel medical advice, and educating health-care providers regarding optimal and accurate malaria prevention recommendations. Providing written instructions to travelers may decrease noncompliance caused by misunderstanding of advice. Because travelers who visit friends or relatives may seek pretravel medical advice through the health-care system less frequently than other tourists, alternative means (e.g., through the travel industry) may be needed to advise these persons. The need for chemoprophylaxis and the choice of antimalarial medication depend on the travel destination (e.g., country of travel or urban versus rural setting); therefore, health-care providers need to elicit a complete travel itinerary before prescribing chemoprophylaxis. In addition, because optimal chemoprophylactic regimens are not 100% effective, patients and physicians need to be aware that prompt diagnostic evaluation should be conducted if symptoms of malaria occur after travel.

Copies of a travelers' information brochure on malaria prevention measures, "Preventing Malaria in Travelers, A Guide for Travelers to Malarious Areas," is available for travel companies and health-care providers and can be obtained by sending a facsimile request to (770) 488-7761. Detailed recommendations for preventing malaria are available 24 hours a day by telephone ({404} 332-4555) or facsimile ({404} 332-4565) from CDC's Malaria Hotline and are published annually in Health Information for International Travel (10), available from the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9235; telephone (202) 512-1800.

Health-care workers are encouraged to consider malaria in the differential diagnosis of fever in persons recently returning from international travel and to report cases to state or local health departments. Consultation on malaria treatment recommendations are available from CDC's Division of Parasitic Diseases, National Center for Infectious Diseases, telephone (770) 488-7760, from 8:00 a.m. to 4:30 p.m. eastern time Monday through Friday and (404) 639-2888 at other hours and on weekends.


  1. Zucker JR, Barber AM, Paxton LA, et al. Malaria surveillance

    • United States, 1992. Atlanta, Georgia: US Department of Health and Human Services, Public Health Service, CDC, 1995.

  2. Zucker JR, Campbell CC. Malaria: principles of prevention and treatment. Infect Dis Clin North Am 1993;7:547-67.

  3. Steffen R, Fuchs E, Schildknecht J, et al. Mefloquine compared with other malaria chemoprophylactic regimens in tourists visiting East Africa. Lancet 1993;341:1299-303.

  4. Lackritz EM, Lobel HO, Howell BJ, Bloland P, Campbell CC. Imported Plasmodium falciparum malaria in American travelers to Africa. JAMA 1991;265:383-5.

  5. Lobel HO, Phillips-Howard PA, Brandling-Bennett AD, et al. Malaria incidence and prevention among European and North American travellers to Kenya. Bull World Health Organ 1990;68:209-15.

  6. Lobel HO, Campbell CC, Pappaioanou M, Huong AY. Use of prophylaxis for malaria by American travelers to Africa and Haiti. JAMA 1987;257:2626-7.

  7. Phillips-Howard PA, Blaze M, Hurn M, Bradley DJ. Malaria prophylaxis: survey of the response of British travellers to prophylactic advice. BMJ 1986;293:932-4.

  8. Bloland PB, Lobel H, Gartner G, Klumpp L, Schwartz I, Campbell CC. Imported Plasmodium falciparum malaria in Americans traveling to Africa: a case follow-up survey. In: Lobel H, Steffen R, Kozarsky PE, eds. Travel medicine 2: proceedings of the Second Conference on International Travel Medicine. Atlanta, Georgia: International Society of Travel Medicine, 1992.

  9. Phillips-Howard PA, Radalowicz A, Mitchell J, Bradley DJ. Risk of malaria in British residents returning from malarious areas. BMJ 1990;300:499-503.

  10. CDC. Health information for international travel, 1995. Atlanta, Georgia: US Department of Health and Human Services, Public Health Service, CDC, 1995; DHHS publication no. (CDC) 94-8280.

Note: To print large tables and graphs users may have to change their printer settings to landscape and use a small font size.

TABLE 1. Number and percentage of reported cases of malaria, by selected characteristics  -- Kentucky *, 1993-1994, Maryland +,
1994, and United  States @, 1993
                                                   1993-1994 Kentucky              1994 Maryland               1993 United States
                                                          (n=16)                       (n=83)                        (n=1275)
                                                  ----------------------          ----------------           -----------------------
Characteristic                                         No.      (%)                 No.      (%)                   No.      (%)
U.S. civilian                                            6    ( 37)                  38    ( 46)                   519     (41)

Proportion of cases acquired by travel                  16    (100)                  83    (100)                  1264     (99)

Plasmodium vivax                                         7    ( 44)                  18    ( 22)                   663     (52)
P. falciparum                                            5    ( 31)                  41    ( 49)                   457     (36)
P. ovale                                                 0       --                   1    (  1)                    41     ( 3)
P. malariae                                              1    (  6)                   5    (  6)                    53     ( 4)
Mixed                                                    2    ( 13)                   0       --                     2     (<1)
Unknown                                                  1    (  6)                  18    ( 22)                    59     ( 5)

Region of acquisition
Africa                                                   7    ( 44)                  53    ( 64)                   745     (58)
Asia                                                     3    ( 19)                  13    ( 16)                   259     (20)
Central America                                          6    ( 38)                   7    (  8)                   146     (11)
Other/Unknown                                            0                           10    ( 12)                   125     (10)

Proportion of U.S. civilians who used                    3    ( 50)                  13    ( 35)                   253     (52)
Correct drug &                                           0    ( 33)                   2    ( 22)                   109     (48)
Correct dose **                                         --                             Unknown                      11     (32)
*  1994 population 3,828,000.
+  1994 population 5,000,000.
@  1994 population 261,523,872.
&  U.S.  Civilians for whom information about use of chemoprophylaxis was available (one of three in Kentucky, two of nine in
   Maryland, and 109 of 225 in the United States).
** U.S. civilians who used a drug recommended by CDC.

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