Malaria diagnosis by NOW ICT and expert microscopy in comparison with multiplex polymerase chain reaction in febrile returned travellers

Excerpt

Malaria is the most potentially dangerous imported parasitic disease in Spain [1, 2] and other European countries [3], and laboratories must be prepared round the clock to diagnose the disease quickly to start treatment and avoid complications [4]. In recent years, a second generation of rapid diagnostic tests combining the detection of a soluble Plasmodium antigen, the histidine-rich protein II (HRP-2) and aldolase, an antigen common to all species of Plasmodium, has been marketed and proved to be useful [5]. As a recent meta-analysis showed that HRP-2-based tests are superior to the lactate dehydrogenase (LDH) tests in diagnosis of malaria in nonimmune returned travellers [6], we decided to perform a multicentric study to determine the performance of a HRP-2-based diagnostic kit (NOW ICT) and expert microscopy in comparison with multiplex polymerase chain reaction (PCR) as the gold standard, with a target population mainly composed of febrile semi- and nonimmune and travellers returned from Africa. Eligible for the study were all febrile patients (> = 38°C),presenting in emergency rooms or ambulatory consults of five hospitals of the Community of Madrid (Spain) who had visited or migrated from an endemic area for malaria in the previous year, to whom the physician in charge requested a malaria test to the laboratory. Patients were excluded if they had received at least one dose of an antimalarial drug in the preceding 4 weeks. Whole-blood samples were collected on ethylenediamine tetraacetic acid (EDTA) tubes for microscopy (thick and thin films stained with Giemsa stain [7]), PCR and HRP-2 detection. The procedure of the NOW ICT (detection of PfHPR2 for P. falciparum and aldolase, a common antigen to the four species of malaria) was performed by laboratory technicians as recommended by the manufacturer [5]. Slides were examined by one experienced microscopist for at least 500 oil fields (x1,000) before reporting them as negative. Parasite count was rated as very low (<250 trophozoites/microliter), low (250–20,000), moderate (20,000–50,000) or high (>50,000). The malaria PCR was carried out in the Parasitology Department of the National Microbiology Center following the seminested multiplex malaria PCR method [8] without knowledge of the results of previous thick film and rapid tests. True positives were defined taking multiplex PCR as the gold standard. Sensitivities and specificities and positive (PPV) and negative (NPV) predictive values with 95% confidence interval (CI) were calculated for expert microscopy and NOW ICT. …