It is important to identify the cause of disease in travelers, not only to treat the individual but also to prevent transmission and to document the prevalence of the specific disease, both in returning travelers and in the countries they visited.
Many travelers' diseases can be identified either by culturing the microorganism, observing it under the microscope, testing for antibodies or antigens, and/or detecting the DNA or RNA of the organism.
- Causes of bacterial diarrhea may be identified with a stool culture and may be treated with antimicrobial agents when symptoms appear and/or may resolve without further tests to identify the pathogen. Some bacterial stool pathogens, such as Shiga-toxin producing E. coli, can be detected by non-culture methods.
- Parasitic causes of diarrhea can be identified through the O&P (ova and parasite) stool test. This test is used to identify parasites and their eggs in a fresh or specially preserved stool sample. For some parasites, such as Giardia intestinalis (lamblia), Entamoeba histolytica, and Cryptosporidia, antigen tests have been developed. These tests identify proteins associated with the parasite and can be useful when parasites are present in low numbers.
- The parasite that causes malaria (Plasmodium spp.) infects red blood cells. It can be identified by collecting a blood sample and examining specially stained "thick and thin" blood smears on slides under the microscope. A rapid antigen assay also has been developed to detect the malaria parasite from a blood sample without a microscopic examination.
- Because identifying the cause of viral diarrhea is complex, viral causes of diarrhea may not be identified by specific cultures or tests unless the virus causes a large number of people to become ill, such as an outbreak of norovirus on a cruise ship.
Tests performed will depend on the disease suspected. People who return from travel with an acute or chronic condition should consult with their doctor, who may suggest a consultation with an infectious disease and/or tropical medicine specialist.
Sometimes x-rays or CT scans may be used to evaluate body organs, such as the lungs or liver, for evidence of infection or damage.