Performance of three rapid diagnostic tests for the detection of Cryptosporidium spp. and Giardia duodenalis in children with severe acute malnutrition and diarrhoea

Background

There is significant need for accurate diagnostic tools for Cryptosporidium spp. and Giardia duodenalis infections in resource limited countries where diarrhoeal disease caused by these parasites is often prevalent. The present study assessed the diagnostic performance of three commercially available rapid diagnostic tests (RDTs) based on faecal-antigen detection for Cryptosporidium spp. and/or G. duodenalis infections in stool samples of children admitted with severe acute malnutrition (SAM) and diarrhoea. An established multiplex PCR was used as reference test.

Methods

Stool samples from children with SAM and diarrhoea enrolled in a randomized controlled trial (registered at clinicaltrials.gov/ct2/show/NCT02246296) in Malawi (n = 175) and Kenya (n = 120) between December 2014 and December 2015 were analysed by a multiplex PCR for the presence of Cryptosporidium spp., G. duodenalis or Entamoeba histolytica parasite DNA. Cryptosporidium-positive samples were species typed using restriction fragment length polymorphism analysis. A sub-sample of the stool specimens (n = 236) was used for testing with three different RDTs. Diagnostic accuracy of the tests under evaluation was assessed using the results of PCR as reference standard using MedCalc software. Pearson Chi-square test and Fisher’s exact test were used to determine (significant) difference between the number of cryptosporidiosis or giardiasis cases found by PCR in Malawi and Kenya. The overall diagnostic accuracy of each RDT was calculated by plotting a receiver operating characteristic (ROC) curve for each test and to determine the area under the curve (AUC) using SPSS8 software.

Results

Prevalence of Cryptosporidium spp. by PCR was 20.0 and 21.7% in Malawi and Kenya respectively, mostly C. hominis. G. duodenalis prevalence was 23.4 and 5.8% in Malawi and Kenya respectively. E. histolytica was not detected by PCR. RDT testing followed the same pattern of prevalence. RDT sensitivities ranged for cryptosporidiosis from 42.9 to 76.9% and for G. duodenalis from 48.2 to 85.7%. RDT specificities ranged from 88.4 to 100% for Cryptosporidium spp. and from 91.2 to 99.2% for G. duodenalis infections. Based on the estimated area under the curve (AUC) values, all tests under evaluation had an acceptable overall diagnostic accuracy (> 0.7), with the exception of one RDT for Cryptosporidium spp. in Malawi.

Conclusions

All three RDTs for Cryptosporidium spp. and Giardia duodenalis evaluated in this study have a moderate sensitivity, but sufficient specificity. The main value of the RDTs is within their rapidness and their usefulness as screening assays in surveys for diarrhoea.

Evaluation of point of care tests for the diagnosis of cutaneous leishmaniasis in Suriname

Background

Cutaneous leishmaniasis (CL) is a serious health problem in Suriname. To expand the diagnostic options, two newly developed diagnostic tests, i.e. the rapid diagnostic test CL Detect™ Rapid Test (CL Detect) and the Loopamp™ Leishmania Detection Kit (Loopamp) were evaluated.

Methods

Diagnostic test performance was compared to the routine diagnostic approach in place, i.e. clinical symptoms combined with microscopy, and to polymerase chain reaction (PCR), which was used as a reference standard. The study population (n = 93) was a typical representation of the CL affected population in Suriname and mainly infected with Leishmania guyanensis.

Results

CL Detect had a very low sensitivity compared to microscopy (36.7%) or PCR (35.8%), due to a high number of false negative results. The specificity of the CL Detect compared to microscopy and PCR was 85.7 and 83.3% respectively. Loopamp sensitivity was 84.8% compared to microscopy and 91.4% compared to PCR. The Loopamp test had a moderate specificity (42.9%) compared to microscopy, but a good specificity compared to PCR (91.7%).

Conclusion

The CL Detect is not likely to be a good replacement for the routine diagnostic procedure for CL in Suriname. The high sensitivity of the easy to perform Loopamp enables the implementation of sensitive molecular diagnosis in resource limited settings.

Evaluation of point-of-care tests for cutaneous leishmaniasis diagnosis in Kabul, Afghanistan

Background

Kabul (Afghanistan) is a major focus of cutaneous leishmaniasis (CL) caused by Leishmania tropica. Microscopy remains the reference test for diagnosis despite its low performance. We evaluated whether Loopamp™ Leishmania Detection Kit (Loopamp) and CL Detect™ Rapid Test (CL Detect), detecting Leishmania DNA and antigen, respectively could improve CL diagnosis.

Methods

A diagnostic accuracy study with prospective inclusion was conducted in a leishmaniasis reference clinic in Kabul. Slit skin samples from CL suspects were analysed by microscopy. Samples taken with a dental broach were tested with CL Detect, Loopamp, and PCR. All samples were transferred to the Academic Medical Center (AMC, the Netherlands) for PCR and Loopamp analyses. The diagnostic performance of the tests was evaluated against a reference combining microscopy and PCR.

Findings

274 CL suspects were included in the study. In Kabul, CL Detect had a 65·4% sensitivity [95% Confidence Interval (CI): 59.2–71.2%] and a 100% specificity [95% CI: 80.5–100%], while these were 87.6% [95%CI: 82.9–91.3%] and 70.6% [95% CI: 44.0–89.7%] for Loopamp. At AMC the Loopamp's sensitivity (92.2% [95% CI: 88.2–95.2%]) and specificity (94.1% [95% CI: 71.3–99.8%]) were higher. An algorithm where CL Detect negative suspects would be tested by Loopamp yielded a 93.4% sensitivity [95% CI: 89.6–96.1%] and a 94.1% specificity [95% CI: 71.3–99.8%] when Loopamp's performance at AMC was used.

Interpretation

The high specificity of CL Detect and the performance of Loopamp allow their use in a diagnostic algorithm that would minimize the number of CL patients referred for confirmation.

Fund

Federal Ministry of Education and Research, Germany.