Limitations of diagnostic tests for bacterial infections.

Lyme disease diagnosis is currently based on serology - an indirect diagnostic method - as laboratory cultures are fastidious. The only direct diagnostic method that can be useful with some specimens (cutaneous biopsies or aspiration fluid) is PCR. We aimed to detail the main limitations of serology and PCR testing in the diagnosis of bacterial infections. Limitations are supported by examples from the recent history of microbiology. The main limitation of bacterial serology is the presence of numerous cross-reactions due to many genes that are common to various bacterial species. Some serological techniques, such as those used for the diagnosis of rickettsioses mainly, have even been based on the existence of cross-reactions. The main limitation of PCR testing is the potential presence of laboratory contaminations. PCR-performing laboratories must therefore be certified for the use of this technique. PCR testing also does not inform on the viability of the identified bacterium and should therefore be interpreted in light of the clinical presentation. These limitations highlight that all diagnostic test results should not be interpreted on their own; the clinical and epidemiological contexts should always be taken into consideration.