Infectious diseases in returning Swedish travellers

The number of travellers to “tropical” parts of the world has increased substantially during the past decades. Identifying risk groups and providing preventive measures is important both to reduce the number of travellers falling ill and to prevent introduction of diseases into new countries. The aim of this thesis is to describe the epidemiology of imported infectious diseases in Sweden and to identify risk groups.

To investigate epidemiology and use of chemoprophylaxis in patients notified with P.falciparum malaria we studied compiled information on patients notified to the Swedish institute for infectious disease control (SMI) 1994-2001. Ninety percent of the patients had traveled to Africa. Malaria infection despite intake of adequate chemoprophylaxis decreased during the study period indicating more effective chemoprophylaxis at the later part of the study. Chloroquine/proguanil had been prescribed for travellers to Africa when it was no longer in line with the national recommendation.

To evaluate risk groups for malaria, we conducted an observational analytic study on all malaria cases notified to SMI 1997-2003 and compared them with data from the Swedish tourist and travel database (TDB). Malaria was more often diagnosed in men than in women (OR 1.7, 95% CI 1.3-2.3), in the age group 0-6 years (OR 4.8, 95% 1.5- 14-8) and in travellers to sub Saharan Africa.

To evaluate the effectiveness and adverse events (AE) of malaria chemoprophylaxis in a high transmission area, we studied compiled information from Swedish soldiers (7,000 person months) in Liberia. The majority (81%) of the soldiers took mefloquine and the remaining part atovaquone/proguanil. After return to Sweden all soldiers completed a questionnaire about behavior and AE. No cases of P. falciparum malaria were notified. The AE were mostly mild. To estimate risk groups for travel related hepatitis A infection in Sweden 1997-2005 we used notification data from SMI as nominator and TDB as a denominator. The highest incidence was seen in the age-group 0-6 years and in travellers to east Africa, Middle East and India where a majority of the travellers had been going to see friends and relatives in their country of origin (VFR-travellers).

To investigate causes of travel related fever we included febrile patients returning from malaria endemic areas to five Swedish hospitals 2005-2008. Additional paired sera were analyzed for influenza virus, dengue virus, chikungunya virus, Brucella spp., Leptospira spp., C.burnetii, and Rickettsia spp. In 21% of patients with unknown fever additional serology revealed a diagnosis. In 9% patients with a defined diagnosis, additional serology established a co-infection. Influenza was the most common serological finding followed by dengue fever, rickettsial infections and leptospirosis.

Conclusion: The chief problem with malariaprophylaxis is the failure to use them when really needed. VFR-travellers, and especially their children, constitute a high risk group for malaria and hepatitis A and preventive measures should be focused on this group. Influenza is an underestimated cause of fever in travellers returning from sub/tropical regions.

List of scientific papers

I. Askling HH, Ekdahl K, Janzon R, Henric Braconier J, Bronner U, Hellgren U, Rombo L, Tegnell A. (2005). Travellers returning to Sweden with falciparum malaria: pre-travel advice, behaviour, chemoprophylaxis and diagnostic delay. Scand J Infect Dis. 37(10): 760-5.
https://doi.org/10.1080/00365540510044120

II. Askling HH, Nilsson J, Tegnell A, Janzon R, Ekdahl K. (2005). Malaria risk in travelers. Emerg Infect Dis. 11(3): 436-41.
https://pubmed.ncbi.nlm.nih.gov/15757560

III. Askling HH, Rombo L, Andersson Y, Martin S, Ekdahl K. (2009). Hepatitis A risk in travelers. J Travel Med. 16(4): 233-8.
https://doi.org/10.1111/j.1708-8305.2009.00307.x

IV. Andersson H, Askling HH, Falck B, Rombo L. (2008). Well-tolerated chemoprophylaxis uniformly prevented Swedish soldiers from Plasmodium falciparum malaria in Liberia, 2004-2006. Mil Med. 173(12): 1194-8.
https://pubmed.ncbi.nlm.nih.gov/19149338

V. Askling HH, Lesko B, Vene S, Berndtson A, Björkman P, Bläckberg J,Bronner U, Follin P, Hellgren U, Palmerus M, Ekdahl K, Tegnell A, Struwe J (1970). Serologic analysis of fever in returned travelers, Sweden. [Accepted]
https://doi.org/10.3201/eid1511.091157