Molecular diagnosis of skin infections using paraffin‐embedded tissue – review and interdisciplinary consensus

Abstract

Summary Nucleic acid amplification techniques (NATs), such as PCR, are highly sensitive and specific methods that have become valuable supplements to culture and serology in the diagnosis of infectious disorders. However, especially when using formalin‐fixed and paraffin‐embedded tissue, these techniques are associated with both false‐negative and false‐positive results, a pitfall that is frequently misjudged. Representatives of the German Society of Hygiene and Microbiology (DGHM) and the German Society of Dermatology (DDG) therefore set out to develop a consensus – in the form of a review article – on the appropriate indications for NATs using paraffin‐embedded tissue, its contraindications, and the key points to be considered in the pre‐ and post‐analytical phase. Given that fresh, naive tissue is preferably to be used in the workup of a suspected infection, PCR analysis on paraffin sections represents an exception. The latter may be considered if an infection is suspected at a later point in time and fresh tissue has not been preserved or can no longer be obtained. Potential indications include confirmation of histologically suspected infections with Leishmania spp., Bartonella spp., Rickettsia spp., or in case of ecthyma contagiosum. Infections with, for example, mycobacteria or RNA viruses, on the other hand, are not considered useful indications for NATs using paraffin sections. In order to avoid misinterpretation of test results, it is essential that laboratory reports on NATs using paraffin‐embedded tissue contain information on the indication/diagnostic circumstances, the required and chosen pre‐analytical steps, the limitations of the method, and on diagnostic alternatives.

Disseminated ulcers with sporotrichoid distribution

“…Biopsy and PCR analysis of fresh tissue are very useful in the event of wound infection, and are fundamental for the microbiological identification of specific pathogens such as mycobacteria [10,11].…”

Disseminierte Ulzera mit sporotrichoider Ausbreitung

“…Biopsie und eine PCR-Analyse von frischem Gewebe sind im Falle einer Wundinfektion sehr hilfreich und für die mikrobiologische Identifikation von spezifischen Krankheitserregern wie Mykobakterien auch von grundlegender Bedeutung [10,11].…”

Diagnosis of mycobacterial skin infections

“…Polymerase chain reaction assays to detect M. leprae have sensitivities that range from 55 % (paucibacillary forms) to 95 % (multibacillary forms) . They may complement the diagnostic armamentarium for suspected leprosy.…”

“…The resulting infiltration is evaluated after 48–72 hours. Due to low sensitivity (33–96 %) and specificity (62 %) and false‐positive results in patients vaccinated with BCG, TST is obsolete for the diagnosis of tuberculosis in adults in developed countries . However, in children as well as in developing countries, the TST is still a cornerstone to test for infection with M. tuberculosis .…”