Typhidot is a laboratory test for typhoid disease, which involves mixing a blood sample with a test reagent and looking for a certain color result. It is a quick and relatively uncomplicated test, which means that doctors, even in some poorer countries, are able to diagnose and treat typhoid rapidly. The basis of the test is that it contains antibodies which bind specifically to the typhoid bacterium to create a positive result.
The bacterial species Salmonella typhi causes typhoid. Typically a problem in regions of the world with inadequate sewage and drinking water infrastructure, typhoid is generally passed through fecal contact from person to person, usually through the contamination of food or water. Potentially fatal, the disease produces a very high fever and requires antibiotic treatment to cure the infection. Many other serious diseases in poor countries, such as malaria, can also cause high fevers, though, so a rapid diagnostic test like Typhidot can be useful to rule these out.
Developed by the Malaysian Bio-Diagnostics Research company, Typhidot is just one of several diagnostic tests on the market to check for the presence of typhoid. According to the World Health Organization, the most accurate way to diagnose typhoid infection is for a doctor to take a bone marrow sample and for a microbiologist to grow any bacteria present in the sample. Isolation of the bacteria is also possible from blood, but the downsides of these tests are that they take a few days and involve much labor and the use of specialized microbiological equipment. In a poor country, the health care system may not be able to afford these tests.
These types of tests rely on traditional microbiological techniques, where bacteria in a sample are allowed to grow in nutrients, until they are present in high enough numbers for the analyst to identify them as specific species. Rapid microbiological tests use newer technology, and do not need to allow time for the initial amount of bacteria in the sample to reproduce. Typhidot, for example, uses a system where any sample containing Salmonella typhi can be identified using antibodies. Antibodies are small molecules produced by the body in response to infection, which stick onto a previously recognized infectious organism and mark it for the body to destroy.
Analysts using the Typhidot test require a small sample of blood from the patient suffering from suspected typhoid fever. They dilute the sample with sterile liquid, and place discs, which the manufacturer has impregnated with antibody that is specific to Salmonella typhi, into the diluted sample. After several incubations and washings of the discs, the discs are soaked with a solution that helps develop color in the presence of the bacterium. A dark color means that Salmonella typhi is present, and absence of color means that the patient is most probably suffering from another disease. The doctor can then give the patient the appropriate treatment for the condition, without having to wait for the longer, although more specific, microbiological test results.