Research
The incidence of malaria in travellers to South-East Asia: is local malaria transmission a useful risk indicator?
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* Corresponding author: Ron H Behrens ron.behrens@lshtm.ac.uk
1 Travel Clinic, Hospital for Tropical Diseases, Mortimer Market, London, WC1E 6JB, UK
2 London School of Hygiene & Tropical Medicine, Clinical Research Unit, London
3 Karolinska Institute, Karolinska University Hospital Huddinge, Department of Infectious Diseases, Stockholm, Sweden
4 Leiden University Medical Centre, Department of Infectious Disease, Section Travel Medicine, Leiden, Netherlands
5 Helsinki University Central Hospital, Department of Medicine, Division of Infectious Diseases, Helsinki, Finland
6 National Malaria Reference Laboratory, Statens Serum Institut, Copenhagen, Denmark
7 Travel Medicine Unit, Division of Infectious Diseases, "Amedeo di Savoia" Hospital, Torino, Italy
8 Section Clinical Tropical Medicine, Department of Infectious Diseases, University Hospital, Heidelberg, Germany
9 Oslo University Hospital, Ullevål, Department of Infectious Diseases, Oslo, Norway
10 Dept of Travel Medicine, Division of Infectious, Barcelona Centre for International Health Research (CRESIB), Hospital Clinic, Barcelona, Spain
11 Medical Department, Swiss Tropical and Public Health Institute, Basel, and Division of Communicable Diseases/Institute for Social and Preventive Medicine, University of Zurich, Zurich, Switzerland
Malaria Journal 2010, 9:266 doi:10.1186/1475-2875-9-266
Published: 4 October 2010Abstract
Background
The presence of ongoing local malaria transmission, identified though local surveillance and reported to regional WHO offices, by S-E Asian countries, forms the basis of national and international chemoprophylaxis recommendations in western countries. The study was designed to examine whether the strategy of using malaria transmission in a local population was an accurate estimate of the malaria threat faced by travellers and a correlate of malaria in returning travellers.
Methods
Malaria endemicity was described from distribution and intensity in the local populations of ten S-E Asian destination countries over the period 2003-2008 from regionally reported cases to WHO offices. Travel acquired malaria was collated from malaria surveillance reports from the USA and 12 European countries over the same period. The numbers of travellers visiting the destination countries was based on immigration and tourism statistics collected on entry of tourists to the destination countries.
Results
In the destination countries, mean malaria rates in endemic countries ranged between 0.01 in Korea to 4:1000 population per year in Lao PDR, with higher regional rates in a number of countries. Malaria cases imported into the 13 countries declined by 47% from 140 cases in 2003 to 66 in 2008. A total of 608 cases (27.3% Plasmodium falciparum (Pf)) were reported over the six years, the largest number acquired in Indonesia, Thailand and Korea. Four countries had an incidence > 1 case per 100,000 traveller visits; Burma (Myanmar), Indonesia, Cambodia and Laos (range 1 to 11.8-case per 100,000 visits). The remaining six countries rates were < 1 case per 100,000 visits. The number of visitors arriving from source countries increased by 60% from 8.5 Million to 13.6 million over the 6 years.
Conclusion
The intensity of malaria transmission particularly sub-national activity did not correlate with the risk of travellers acquiring malaria in the large numbers of arriving visitors. It is proposed to use a threshold incidence of > 1 case per 100,000 visits to consider targeted malaria prophylaxis recommendations to minimize use of chemoprophylaxis for low risk exposure during visits to S-E Asia. Policy needs to be adjusted regularly to reflect the changing risk.