Acid-fast bodies in faecal smears stained by the modified Ziehl-Neelsen technique

The modified Ziehl-Neelsen (ZN) stain has proved useful in the laboratory diagnosis of cryptosporidiosis and, more recently, for the laboratory diagnosis of cyclospora. Apart from cryptosporidia and cyclospora, many other organisms and artefacts are present in faeces, and may be seen in faecal smears stained by the modified ZN method. Described here is the presence of such organisms and artefacts in faecal samples submitted to the routine microbiology laboratory of a district general hospital. Over 6000 faecal smears were examined using the modified ZN method, with an incidence of cyclospora and cryptosporidium of approximately 0.1% and 1%, respectively. Other organisms and artefacts were observed, with an incidence ranging from 0.1% to 1%. It is emphasised that the identification of known gastrointestinal tract pathogens should not rely solely on the results of their staining reactions. It is essential that criteria such as morphology and size be taken into account to differentiate organisms with similar staining reactions.