Diagnostic accuracy of a LAMP kit for diagnosis of imported malaria in Switzerland

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Summary

Background

The diagnosis of acute malaria in non-endemic countries is still carried out largely by microscopic examination of thick and thin smears or rapid diagnostic tests. Low-density infections might be missed, however, but the more sensitive PCR is more expensive, complex and requires considerable more time.

Method

We examined the suitability of a new loop-mediated isothermal DNA-amplification kit (LAMP) for malaria diagnosis in febrile returning travellers in comparison to qPCR and microscopic examination in a prospective study in a non-endemic setting at the Swiss TPH.

Results

Among 205 complete datasets, 43 samples were positive for malaria by microscopy, with Plasmodium falciparum (35 cases) being the most frequent species. All these samples were positive by both LAMP and qPCR, too. An additional 4 samples negative by microscopy were positive by both LAMP and qPCR. Three of these samples were follow-up samples taken after start of treatment in patients originally identified as positive by microscopy.

Conclusions

The LAMP performed exactly as did the qPCR and is a very valuable diagnostic alternative with a potential of being used also in endemic settings.

Introduction

The diagnosis of malaria remains a challenge in endemic as well as in non-endemic countries, where imported cases in returning travellers or in migrants require a rapid and accurate diagnosis. The unfortunately often low quality of microscopic examinations of thick and thin smears in highly endemic areas [1] can at least in some settings be overcome by the use of rapid diagnostic tests (RDTs) in combination with a good clinical algorithm [2]. In non-endemic settings, however, also low-level parasitemias below the detection limit of RDTs have to be reliably diagnosed in order to avoid a potentially fatal misdiagnosis. Expert microscopy is more sensitive than RDTs, but takes about 60 min to yield a reliable result and is not always available and difficult to sustain. PCR has been shown to have a clearly higher sensitivity and specificity than expert microscopy [3], but the expensive equipment as well as the time required for testing (several hours for qPCR) are major drawbacks for a wide-scale use. The development of the loop-mediated isothermal DNA-amplification (LAMP) technique, which uses a closed system with a reading carried out by the naked eye, allows to speed up the diagnostic procedure to the time of a microscopic examination, while achieving the same diagnostic sensitivity as PCR. The ease of handling, the speed and the high sensitivity make LAMP an ideal alternative for diagnosing malaria in travellers and migrants. LAMP has been developed for several parasitic infections, and a kit for malaria diagnosis that is stable at ambient temperature has been commercialised. This kit was evaluated in an European hospital setting in a specialist parasitology laboratory investigating blood samples from suspected imported malaria cases, showing a diagnostic performance similar to PCR and superior to microscopy [4].

Our aim was to evaluate the performance of the LAMP for malaria in a different setting and using an alternative method for sample processing. The diagnostic laboratory of the Swiss TPH as the Swiss reference laboratory for imported parasitoses, is not attached to a hospital, but receives samples for testing largely by postal service and to a smaller extent from the patients at the outpatient department (OPD) of the Swiss TPH. Blood samples sent in from hospitals, private practitioners or other laboratories for examination are anticoagulated with EDTA, which will, however, not work with the PURE device recommended by the manufacturer of the LAMP kit for extraction of DNA. We adapted the method to using the QIAmp DNA kit instead and wanted to determine the performance of the adapted methodology.

Section snippets

Ethical considerations

The study was approved by the joint Ethics Committee of the Cantons of Basel-Stadt and Baselland (EK number 23/12, dated February 7th 2012), Switzerland. Study staff was trained referring to the protocol and relevant study procedures during 3 days prior to the start of the study. Patients were orally informed about the ongoing study by the staff. They then received detailed written information before venipuncture and were only included in the study if they signed the informed consent. If they

Results

A total of 210 samples with a request for examination for malaria were included in the study. Males represented 55.7% of the study subjects (n = 117). The median age for males was 37 years (range 10 months–75 years) and for females 35 years (range 8 months–78 years). Five samples had to be excluded because there was not enough blood for all the tests or the heparinized sample was missing (Fig. 1). So a total of 205 samples with all tests completed were included in the analysis. Travel history

Discussion

The quest for fast, cheap and more sensitive alternatives to microscopic examination for diagnosis of malaria is still on after the introduction of qPCR and RDTs. While qPCR is very sensitive, it needs expensive equipment and is complex. The fast and cheap RDTs instead are readily available in many different formats. Although the performance of these tests is often judged as equal or even superior to microscopy [5], other studies show that they could still be improved on their sensitivity,

Conflict of interests

HM and CS have no conflict of interest to declare. IG is an employee of FIND, a co-developer of the malaria LAMP kit.

Acknowledgement

We thank to all voluntary participants in the study and to Michelle Dobler for her expert technical assistance.

This work was supported by the Foundation for Innovative New Diagnostics (FIND) with funds from the German Federal Ministry of Education and Research (BMBF, Grant number 2020 60 47) through the KfW Entwicklungsbank.

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