Detection of trypanosomes in suspected sleeping sickness patients in Uganda using the polymerase chain reaction

Diagnosis of sleeping sickness (trypanosomiasis) is difficult because of th e fluctuating levels of parasitaemia encountered in patients. In the presen t study we found that the polymerase chain reaction (PCR) demonstrated tryp anosome infection in 20 out of 35 (57.1%) blood samples and in 21 out of 34 (61.7%) cerebrospinal fluid (CSF) samples collected from an area endemic f or sleeping sickness in north-west Uganda. A total of 14 blood samples and 13 CSF samples that were positive for trypanosomes by double centrifugation were also positive by PCR, demonstrating good concordance between the two methods. However, 6 (28.6%) of the 21 blood samples that were parasitologic ally negative were positive by PCR, while 8 (38.0%) out of 21 CSF samples t hat were negative by double centrifugation were positive by PCR. These 14 n egative samples could therefore be from sleeping sickness cases even though a positive PCR test is not evidence for the presence of trypanosomes. Furt hermore, of these 8 CSF samples, 4 had been designated as early cases, base d on the absence of trypanosomes and on a count of less than or equal to 5 white blood cells (WBC) per mu l. This suggests that some late-stage cases could potentially be missed according to the present criteria, and it is th erefore important to perform clinical trials to determine whether these cas es could be treated successfully with the first-stage drug alone. The remai ning four CSF samples had been classified as late-stage cases, based on a c ount of > 6 WBC per mu l, even though trypanosomes could not be detected in these samples by either double centrifugation or PCR. A cut-off point of 5 WBC per mu l, which is used as a rule of thumb to stage sleeping sickness patients, seems to leave some late-stage cases undetected since trypanosome s were detected in four CSF samples from suspected cases with < 5 WBC per m u l.