Practical Guidance for Clinical Microbiology Laboratories: Laboratory Diagnosis of Parasites from the Gastrointestinal Tract

This Practical Guidance for Clinical Microbiology document on the laboratory diagnosis of parasites from the gastrointestinal tract provides practical information for the recovery and identification of relevant human parasites. The document is based on a comprehensive literature review and expert consensus on relevant diagnostic methods. However, it does not include didactic information on human parasite life cycles, organism morphology, clinical disease, pathogenesis, treatment, or epidemiology and prevention. As greater emphasis is placed on neglected tropical diseases, it becomes highly probable that patients with gastrointestinal parasitic infections will become more widely recognized in areas where parasites are endemic and not endemic. Generally, these methods are nonautomated and require extensive bench experience for accurate performance and interpretation.

Malaria "epidemic" in Quebec: diagnosis and response to imported malaria.

BACKGROUND: Imported malaria is an increasing problem. The arrival of 224 African refugees presented the opportunity to investigate the diagnosis and management of imported malaria within the Quebec health care system. METHODS: The refugees were visited at home 3-4 months after arrival in Quebec. For 221, a questionnaire was completed and permission obtained for access to health records; a blood sample for malaria testing was obtained from 210. RESULTS: Most of the 221 refugees (161 [73%]) had had at least 1 episode of malaria while in the refugee camps. Since arrival in Canada, 87 (39%) had had symptoms compatible with malaria for which medical care was sought. Complete or partial records were obtained for 66 of these refugees and for 2 asymptomatic adults whose children were found to have malaria: malaria had been appropriately investigated in 55 (81%); no malaria smear was requested for the other 13. Smears were reported as positive for 20 but confirmed for only 15 of the 55; appropriate therapy was verified for 10 of the 15. Of the 5 patients with a false-positive diagnosis of malaria, at least 3 received unnecessary therapy. Polymerase chain reaction testing of the blood sample obtained at the home visit revealed malaria parasites in 48 of the 210 refugees (23%; 95% confidence interval [CI] 17%- 29%). The rate of parasite detection was more than twice as high among the 19 refugees whose smears were reported as negative but not sent for confirmation (47%; 95% CI 25%- 71%). INTERPRETATION: This study has demonstrated errors of both omission and commission in the response to refugees presenting with possible malaria. Smears were not consistently requested for patients whose presenting complaints were not "typical" of malaria, and a large proportion of smears read locally as "negative" were not sent for confirmation. Further effort is required to ensure optimal malaria diagnosis and care in such high-risk populations.

Malaria epidemics and surveillance systems in Canada.

In the past decade, fluctuations in numbers of imported malaria cases have been seen in Canada. In 1997 to 1998, malaria case numbers more than doubled before returning to normal. This increase was not seen in any other industrialized country. The Canadian federal malaria surveillance system collects insufficient data to interpret these fluctuations. Using local (sentinel), provincial, federal, and international malaria surveillance data, we evaluate and interpret these fluctuations. Several epidemics are described. With an ever-increasing immigrant and refugee population of tropical origin, improved surveillance will be necessary to guide public health prevention policy and practice. The Canadian experience is likely to be generalizable to other industrialized countries where malaria is a reportable disease within a passive surveillance system.

Comparison of blood smear, antigen detection, and nested-PCR methods for screening refugees from regions where malaria is endemic after a malaria outbreak in Quebec, Canada.

The importation of malaria into a region where it is not endemic raises many concerns, including the timely delivery of appropriate care, safety of the blood supply, and the risk of autochthonous transmission. There is presently no consensus on the best way to screen mobile populations for malaria. Between August 2000 and March 2001, 535 refugees arrived in Quebec, Canada, from Tanzanian camps. Within 4 weeks of resettlement of the first group of 224, the McGill University Centre for Tropical Diseases noted an outbreak of malaria across the province (15 cases over a 3-week period). This group (group 1) was traced and screened for malaria between 3 and 4 months after arrival in Canada. Subsequent groups of 106 and 205 refugees were screened immediately upon arrival in Canada (group 2) and immediately prior to their departure from refugee camps (group 3), respectively. A single EDTA-blood sample was obtained from 521 refugees for testing by thick and thin blood smears (groups 1 and 2), antigen detection (ICT Malaria Pf and OptiMAL; group 1 only), and nested PCR (all groups). Overall, 98 of 521 refugees were found to be infected (18.8%). The vast majority of infections (81 of 98) were caused by Plasmodium falciparum alone. Using PCR as the "gold standard," both microscopy (sensitivity, 50%; specificity, 100%) and antigen detection (ICT sensitivity, 37.5%; ICT specificity, 100%; OptiMAL sensitivity, 29.1%; OptiMAL specificity, 95.6%) performed poorly. None of the PCR-positive subjects were symptomatic at the time of testing, and only two had recently had symptoms compatible with malaria (with or without diagnosis and treatment). Active surveillance of migrants from regions of intense malaria transmission can reduce the risk of morbidity in the migrant population and mitigate against transmission to the host population. Our data demonstrate that PCR is, by far, the most powerful tool for such surveillance.