Optimization of routine microscopic and molecular detection of parasitic protozoa in SAF-fixed faecal samples in Sweden.

Background

Nucleic acid-based methods are increasingly used for screening of gastrointestinal parasites. Microscopy is still used and Swedish routine protocol consists of formalin ethyl-acetate concentration and do not include screening for trophozoites or Cryptosporidium spp. This study aimed to compare detection with the Swedish routine microscopy method to an extended method that includes screening for trophozoites and Cryptosporidium. Furthermore, we also developed a method for DNA recovery from SAF-fixed faecal samples and compared the real-time PCR detection of Giardia intestinalis, Dientamoeba fragilis, Cryptosporidium spp., Entamoeba histolytica and Entamoeba dispar from SAF-fixed and unpreserved faecal samples. PCR results were then compared with microscopy results.

Methods

SAF-fixed and unpreserved faecal samples from 1000 patients at the Clinical microbiology laboratory in Region Jönköping County, Sweden, were included. Samples were analysed with routine formalin ethyl-acetate concentration, wet mounts from both concentrated and unconcentrated samples, Ziehl-Neelsen staining on patients with certain symptoms and real-time PCR.

Results

We found a significant higher detection rate of parasites with the extended microscopy method compared to the Swedish routine microscopy method when SAF-fixed samples were used. The detection rate with real-time PCR in SAF-fixed samples was equal to the detection rate in unpreserved samples. There was no significant difference in detection comparing extended microscopy and real-time PCR.

Conclusion

In conclusion, this study showed that the extended microscopy method increased detection of intestinal protozoa with detection of both trophozoites and Cryptosporidium spp. We also showed that SAF-fixative can be used for detection of parasite-DNA with real-time PCR.