PCR in meningoencephalitis diagnosis.

Polymerase chain reaction (PCR) detection of a stretch of nucleic acid sequence of microbial origin from a clinical sample is not always diagnostic of disease unless the identified agent is a strict pathogen or its growth is documented. We describe here a case of acute meningoencephalitis in a 21-y-old man, in whom no pathogen was isolated by traditional bacterial or viral culture. Standard DNA PCR performed on the cerebrospinal fluid (CSF) identified the presence of 3 infectious agents: HHV-6, HHV-7 and Mycoplasma pneumoniae. Additional PCRs performed on CSF fractions along with gene transcript analysis proved the bystander role of the 2 herpesviruses and indicated M. pneumoniae as the relevant replicating agent, most likely playing to be a pathogenic role. Until this useful analysis becomes routine, clinicians should deal carefully with DNA PCR results, especially when assessing the aetiological role of agents , such as herpesviruses, which are known to undergo latency.