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 d iagnosis of cryptosporidiosis and, more recently, for the laboratory diagno sis of cyclospora. Apart from cryptosporidia and cyclospora, many other org anisms and artefacts are present in faeces, and may be seen in faecal smear s stained by the modified ZN method. Described here is the presence of such organisms and artefacts in faecal samples submitted to the routine microbi ology laboratory of a district general hospital. Over 6000 faecal smears we re examined using the modified ZN method, with an incidence of cyclospora a nd cryptosporidium of approximately 0.1% and 1%, respectively. Other organi sms and artefacts were observed, with an incidence ranging from 0.1% to 1%. It is emphasised that the identification of known gastrointestinal tract p athogens should not rely solely on the results of their staining reactions. It is essential that criteria such as morphology and size be taken into ac count to differentiate organisms with similar staining reactions.