Evaluation of the OptiMAL Test for Rapid Diagnosis of Plasmodium vivax and Plasmodium falciparum Malaria

The development of rapid and specific diagnostic tests to identify individuals infected with malaria is of paramount importance in efforts to control the severe public health impact of this disease. This study evaluated the ability of a newly developed rapid malaria diagnostic test, OptiMAL (Flow Inc., Portland, Oreg.), to detect Plasmodium vivax and Plasmodium falciparum malaria during an outbreak in Honduras. OptiMAL is a rapid (10-min) malaria detection test which utilizes a dipstick coated with monoclonal antibodies against the intracellular metabolic enzyme parasite lactate dehydrogenase (pLDH). Differentiation of malaria parasites is based on antigenic differences between the pLDH isoforms. Since pLDH is produced only by live Plasmodium parasites, this test has the ability to differentiate live from dead organisms. Results from the OptiMAL test were compared to those obtained by reading 100 fields of traditional Giemsa-stained thick-smear blood films. Whole-blood samples were obtained from 202 patients suspected of having malaria. A total of 96 samples (48%) were positive by blood films, while 91 (45%) were positive by the OptiMAL test. The blood films indicated that 82% (79 of 96) of the patients were positive for P. vivax and 18% (17 of 96) were infected with P. falciparum. The OptiMAL test showed that 81% (74 of 91) were positive for P. vivax and 19% (17 of 91) were positive for P. falciparum. These results demonstrated that the OptiMAL test had sensitivities of 94 and 88% and specificities of 100 and 99%, respectively, when compared to traditional blood films for the detection of P. vivax and P. falciparum malaria. Blood samples not identified by OptiMAL as malaria positive normally contained parasites at concentrations of less than 100/μl of blood. Samples found to contain P. falciparum were further tested by two other commercially available rapid malaria diagnostic tests, ParaSight-F (Becton Dickinson, Cockeysville, Md.) and ICT Malaria P.f. (ICT Diagnostics, Sydney, Australia), both of which detect only P. falciparum. Only 11 of the 17 (65%) P. falciparum-positive blood samples were identified by the ICT and ParaSight-F tests. Thus, OptiMAL correctly identified P. falciparum malaria parasites in patient blood samples more often than did the other two commercially available diagnostic tests and showed an excellent correlation with traditional blood films in the identification of both P. vivax malaria and P. falciparum malaria. We conclude that the OptiMAL test is an effective tool for the rapid diagnosis of malaria.     

Comparison of two commercial assays with expert microscopy for confirmation of symptomatically diagnosed malaria

Conventional light microscopy has been the established method for malaria diagnosis. However, recently several nonmicroscopic rapid diagnostic tests have been developed for situations in which reliable microscopy may not be available. This study was conducted to evaluate the diagnostic performance of a recently introduced ICT Malaria Pf/Pv test. This assay detects Plasmodium falciparum histidine-rich protein 2 antigen (PfHRP-2) for P. falciparum diagnosis and pan-malarial antigen for P. vivax diagnosis. In this study we compared the performance of ICT Malaria Pf/Pv with microscopy of Giemsa-stained blood films and with an OptiMAL test that detects Plasmodium lactate dehydrogenase (pLDH) antigen. A total of 750 clinically suspected malaria patients were examined at local health centers in Kuwait. Both the antigen tests had a high degree of specificity (>98%) for detection of malaria infection. However, they were less sensitive than microscopy. Compared with microscopy the ICT Malaria PF/pf test failed to detect malaria infection in 93 (34%) of 271 malaria patients (11% of patients with P. falciparum and 37% of patients with P. vivax) and the OptiMAL test failed to detect malaria infection in 41 (15%) of 271 malaria patients (7% of patients with P. falciparum and 13% of patients with P. vivax). The sensitivities of the ICT Malaria Pf/Pv and OptiMAL tests for detection of P. falciparum infection were 81 and 87%, and those for detecting P. vivax were 58 to 79%, respectively. The sensitivity of the ICT Malaria Pf/Pv and OptiMAL tests decreased significantly to 23 and 44%, respectively, at parasite densities of <500/ micro l. Both of the tests also produced a number of false-positive results. Overall, the performance of the OptiMAL test was better than that of the ICT Malaria Pf/Pv test. However, our results raise particular concern over the sensitivity of the ICT Malaria Pf/Pv test for detection of P. vivax infection. Further developments appear necessary to improve the performance of the ICT Malaria Pf/Pv test.     

Plasmodium falciparum histidine-rich protein 2-based immunocapture diagnostic assay for malaria: cross-reactivity with rheumatoid factors

Recently introduced rapid nonmicroscopic immunocapture assays for the diagnosis of malaria infection are being evaluated for their sensitivity and specificity in various epidemiological settings. A Plasmodium falciparum histidine-rich protein 2 (PfHRP-2)-based assay (ICT) and a Plasmodium-specific lactate dehydrogenase test (OptiMAL) were evaluated for their specificities in different groups of patients who tested negative for malaria infection by microscopy. The patients were selected from different disease groups: rheumatoid arthritis, hepatitis C, toxoplasmosis, schistosomiasis, and hydatid disease. One hundred thirty-three of the 225 patients were positive for rheumatoid factor. Thirty-five of the 133 (26%) rheumatoid factor-positive patients gave a false-positive reaction with the ICT assay, but only 4 of these gave false-positive reactions with the OptiMAL test. Thirty-three of the 35 false-positive specimens became negative when repeat tested with the ICT assay after absorbing out the rheumatoid factor activity. Our study shows that the PfHRP-2-based ICT assay gave a false-positive reaction in 26% of the patients who had rheumatoid factors, but were negative for malaria by microscopy.     

Non-microscopic method for malaria diagnosis using OptiMAL IT,a second-generation dipstick for malaria pLDH antigen detection

Rapid diagnostic tests for malaria are now a commonly used procedure for malaria diagnosis. New or improved devices need to be evaluated against a recognised gold-standard procedure and subjected to conditions of temperature and humidity that may affect their performance. The OptiMAL 48 RDT has now been available commercially for several years and a second-generation OptiMAL IT test is now coming onto the market. In this study the problems associated with the routine use of OptiMAL 48 is investigated and its performance compared with a second-generation individual test, OptiMAL IT. Sensitivity and specificity for detection of all malaria species for both tests were comparable but loss of sensitivity of the test strips due to humidity or temperature found with the routine use of OptiMAL 48 was not seen with the individual OptiMAL IT. False-positive results for Plasmodium falciparum, seen in two negative blood samples, were attributed to the presence of high levels of heterophile antibodies.     

Multicenter study to evaluate the OptiMAL test for rapid diagnosis of malaria in U.S. hospitals

More than 1,000 cases of malaria are diagnosed each year in the United States. Reported numbers, however, may be artificially low because many clinicians fail to consider the diagnosis on presentation, U.S. hospital laboratory technologists have very limited experience in detecting and identifying malaria parasites, and reporting of malaria to state health departments is sporadic in many states. In this study, a rapid malaria diagnostic test, the OptiMAL test (DiaMed; under license from Flow Inc., Portland, Oreg.) was evaluated in six U.S. hospitals and compared with results of microscopy. The OptiMAL test is a 15-min rapid immunochromatographic test that both identifies and differentiates Plasmodium falciparum from non-P. falciparum malaria parasites on the basis of the detection of parasite lactate dehydrogenase in a drop of patient blood. A total of 216 specimens from patients suspected of having malaria were tested. Results indicated that 43 samples (20%) were positive for malaria parasites by microscopy (32 P. falciparum, 11 non-P. falciparum) while 42 (19%) were positive by OptiMAL (31 P. falciparum, 11 non-P. falciparum). The sensitivity of the OptiMAL test was 98%; its specificity was 100%, with positive and negative predictive values of 100 and 99%, respectively. Participating hospital physicians and laboratory directors independently reported that the OptiMAL rapid malaria test was accurate, easy to use, and well accepted by those working in their diagnostic laboratories. The overall conclusion was that integration of the OptiMAL rapid malaria test into the U.S. health care infrastructure would provide an important and easy-to-use tool for the timely diagnosis of malaria.     

Comparison of three real-time PCR methods with blood smears and rapid diagnostic test in Plasmodium sp. infection

In cases of malaria, rapid and accurate diagnosis of Plasmodium sp. is essential. In this study three different quantitative, real-time PCR methods were compared with routine methods used for malaria diagnosis. A comparative study was conducted prospectively in the laboratories of Montpellier and Nîmes University Hospitals. The methods used for routine diagnostic malaria testing consisted of microscopic examination of Giemsa-stained blood smears and rapid diagnostic tests. Three quantitative real-time PCR methods (qRT-PCR) were tested: qRT-PCR1 amplified a specific sequence on the P. falciparum Cox1 gene, qRT-PCR2 amplified a species-specific region of the multicopy 18S rDNA, and qRT-PCR3 amplified a mitochondrial DNA sequence. Among the 196 blood samples collected, 73 samples were positive in at least one of the five tests. Compared with the routine method, there were no false negatives for P. falciparum diagnosis in either qRT-PCR1 or qRT-PCR3. In all P. ovale, P. vivax and P. malariae infections diagnosed from blood smears, qRT-PCR1 was negative, as expected, whereas qRT-PCR2 and qRT-PCR3 were positive and concordant (simple κ coefficient = 1). One negative sample from microscopy was positive with both qRT-PCR2 and qRT-PCR3. Together, qRT-PCR3 and the combined qRT-PCR1 and qRT-PCR2 were concordant with routine methods for malaria diagnosis (99% and 99.5%, respectively). These three rapid, molecular qRT-PCR methods, used alone or in association, showed excellent results, with high concordance, accuracy and reliability in malaria diagnosis.     

Performance of an immunochromatographic test for the rapid diagnosis of malaria

The immunochromatographic test (ICT) for the rapid diagnosis of malaria has been marketed for several years. In a study in which three Centres of Tropical Medicine participated and data were pooled, performance of the test varied considerably when comparing the results between each centre. The sensitivity of ICT in 2,343 patients tested in our services was 100% and the specificity 99.74%. Moreover, two patients with a positive ICT would initially have been missed by expert microscopy, with Plasmodium falciparum malaria being confirmed microscopically some hours later. The principal reasons for the better performance of the test in our series appear to be blood collection in EDTA vials and considerable experience with handling and interpreting the ICT test.     

Malaria rapid diagnostic tests in travel medicine

Malaria is a serious condition in the non-immune traveller, and prognosis depends on timely diagnosis. Although microscopy remains the cornerstone of diagnosis, malaria rapid diagnostic tests (RDTs) are increasingly used in non-endemic settings. They are easy to use, provide results rapidly and require no specific training and equipment. Reported sensitivities vary between different RDT products but are generally good for Plasmodium falciparum, with RDTs detecting the P. falciparum antigen histidine-rich protein-2 (PfHRP2) scoring slightly better than P. falciparumlactate dehydrogenase (Pf-pLDH)-detecting RDTs. Sensitivity is lower for Plasmodium vivax (66.0 – 88.0%) and poor for Plasmodium ovale (5.5 – 86.7%) and Plasmodium malariae (21.4 – 45.2%). Rapid diagnostic tests have several other limitations, including persistence of the PfHRP2 antigen, cross-reactions of P. falciparum with the non-falciparum test line and vice versa and (rare) false-positive reactions due to other infectious agents or immunological factors. False-negative results occur in the case of low parasite densities, prozone effect or pfhrp2 gene deletions. In addition, errors in interpretation occur, partly due to inadequacies in the instructions for use. Finally, RDTs do not give information about parasite density. In the diagnostic laboratory, RDTs are a valuable adjunct to (but not a replacement for) microscopy for the diagnosis of malaria in the returned traveller.In malaria endemic settings, special groups of travellers (those travelling for long periods, expatriates and short-stay frequent travellers) who are remote from qualified medical services may benefit from self-diagnosis by RDTs, provided they use correctly stored RDT products of proven accuracy, with comprehensive instructions for use and appropriate hands-on training.     

Evaluation of rapid diagnostic tests for malaria in Swedish travellers

Rapid diagnostic tests (RDTs) for malaria have become valuable tools for the diagnosis of malaria in both endemic and non-endemic areas. During a 7-year period, first the MalaQuick rapid test and then the NOW Malaria test, were evaluated by well-trained laboratory technicians in a university hospital laboratory of parasitology. A total of 635 blood samples were selected from 4731 blood specimens obtained from travellers at the emergency department, at wards and at out-patient clinics. The samples were analysed by microscopy and RDT. Malaria parasites were detected in the blood films of 134 (21%) samples. The sensitivity of the RDT for Plasmodium falciparum was 97.7% (84 of 86 samples) with a negative predictive value of 99.6%. The two false-negative results were associated with low levels of parasitaemia. For non-falciparum species the sensitivity was only 58.3% (28 of 48 samples). Based on the excellent ability of the RDTs to detect P. falciparum infections, we recommend the use of the NOW Malaria test as a complement to microscopy in the laboratory.     

Study and evaluation of Wondfo rapid diagnostic kit based on nano-gold immunochromatography assay for diagnosis of <Emphasis Type="BoldItalic">Plasmodium falciparum</Emphasis>

Malaria has been recognized as a human disease for thousands of years and remains one of the most common diseases affecting humans worldwide. Therefore, a method for rapidly detecting Plasmodium falciparum is necessary and useful. We have developed Wondfo rapid diagnostic kit based on nano-gold immunochromatography assay for the detection of P. falciparum in patient specimen. In the present study, we demonstrated the sensitivity and specificity of the rapid diagnostic kit in which nano-gold labeling techniques and the monoclonal antibodies against histidine-rich protein-2 of P. falciparum were used to establish two-antibody sandwich immunochromatographic assay for detecting P. falciparum. By using microscopic examination of blood smears as control, the sensitivity, specificity, and feasibility of Wondfo rapid diagnostic kit was determined in the prompt and accurate diagnosis of malaria. In this study, 1,558 blood samples were collected from outpatient clinics in China and detected by both Wondfo kit and microscopic examination. The Wondfo kit did not show cross-reaction with microfilaria, Toxoplasma gondii, and other parasites in the blood. The patient samples positive for rheumatoid factor, HIV, tuberculosis, and syphilis did not show false positivity when testing with Wondfo kit. The detection sensitivity and specificity of Wondfo rapid diagnostic kit were 95.49% and 99.53%, respectively. These results indicate that our rapid diagnostic assay may be useful for detecting P. falciparum in patient specimen.     

A Quality Control Program within a Clinical Trial Consortium for PCR Protocols To Detect Plasmodium Species

Malaria parasite infections that are only detectable by molecular methods are highly prevalent and represent a potential transmission reservoir. The methods used to detect these infections are not standardized, and their operating characteristics are often unknown. We designed a proficiency panel of Plasmodium spp. in order to compare the accuracy of parasite detection of molecular protocols used by labs in a clinical trial consortium. Ten dried blood spots (DBSs) were assembled that contained P. falciparum, P. vivax, P. malariae, and P. ovale; DBSs contained either a single species or a species mixed with P. falciparum. DBS panels were tested in 9 participating laboratories in a masked fashion. Of 90 tests, 68 (75.6%) were correct; there were 20 false-negative results and 2 false positives. The detection rate was 77.8% (49/63) for P. falciparum, 91.7% (11/12) for P. vivax, 83.3% (10/12) for P. malariae, and 70% (7/10) for P. ovale. Most false-negative P. falciparum results were from samples with an estimated ≤5 parasites per μl of blood. Between labs, accuracy ranged from 100% to 50%. In one lab, the inability to detect species in mixed-species infections prompted a redesign and improvement of the assay. Most PCR-based protocols were able to detect P. falciparum and P. vivax at higher densities, but these assays may not reliably detect parasites in samples with low P. falciparum densities. Accordingly, formal quality assurance for PCR should be employed whenever this method is used for diagnosis or surveillance. Such efforts will be important if PCR is to be widely employed to assist malaria elimination efforts.     

High-Sensitivity Detection of Human Malaria Parasites by the Use of Rapid Diagnostic Tests and Nested Polymerase Chain Reaction in Burdened Communities of North East India

Background and Objectives: The study aimed to evaluate the diagnostic performance of malaria through microscopy and rapid diagnostic test (RDT) analysis performed locally and the accuracy evaluated by nested polymerase chain reaction (PCR) for diagnosis of Plasmodium falciparum from hotspot regions of North East (NE) India. Materials and Methods: One thousand one hundred and seventy-three blood samples were collected for identification of P. falciparum infection using microscopy and RDT analysis. DNA was extracted from whole blood using QIAamp DNA blood mini kit, and nested PCR was performed to confirm P. falciparum for evaluating sensitivity and specificity from various epidemiological surveys and geographical areas of NE India. Results: Of 1173 symptomatic malaria suspected patients, 15.6% (183/1173) patients were diagnosed as malaria positive by RDT and 67.94% cases (53/78) with microscopy. Of 183 malaria-positive patients, 42.62% (78/183) were diagnosed with P. falciparum and 84.61% (66/78) further confirmed to be P. falciparum positive by nested PCR. High sensitivity (97.9%) and low specificity (2.03%) of the RDT and high sensitivity (99.1%) and low specificity (0.9%) in microscopy against nested PCR results was statistically significant (P < 0.05). Epidemiological comparisons expressed highest incidences in Manipur (51.11%) followed by Meghalaya (48.93%) and Assam (35.16%). Overall incidence rate among the genders was observed to be higher in males than in females. Conclusions: Our findings suggest that PCR, RDT and microscopy can potentially determine hotspots at moderate transmission intensities, but PCR testing has a diagnostic advantage as transmission intensity falls. Therefore, malaria control programs should consider PCR testing when the prevalence of infection is low.     

False-Positive Results for Rapid Diagnostic Tests for Malaria in Patients with Rheumatoid Factor

Four different rapid diagnostic tests (RDTs) for malaria were evaluated by testing 82 healthy control patients, 89 Plasmodium vivax-infected patients, and 92 rheumatoid factor (RF)-positive nonmalaria patients. The false-positive rate ranged from 2.2% to 13% in RF-positive patients. High RF levels are associated with malaria RDT false positivity.     

Detection and species determination of malaria parasites by PCR: comparison with microscopy and with ParaSight-F and ICT malaria Pf tests in a clinical environment

A rapid procedure for the diagnosis of malaria infections directly from dried blood spots by PCR amplification was evaluated with samples from 52 patients. Plasmodium infections were identified with a genus-specific primer set, and species differentiation between Plasmodium falciparum and Plasmodium vivax was analyzed by multiplex PCR. The PCR test with any of the three primer sets was able to detect as few as four parasites per microliter by gel electrophoresis or by nonisotopic paper hybridization chromatography. The diagnoses obtained by PCR correlated closely with those obtained by Giemsa staining except for two samples observed to have mixed P. falciparum-P. vivax infections. These were initially missed by microscopic analysis. In comparison with antigen-capture assays for P. falciparum, the PCR assays were able to detect three infections that were missed by the ParaSight-F test. The PCR test was negative for nine ParaSight-F-positive samples and one ICT Malaria Pf-positive sample, and these were confirmed to be false-positive results. The PCR thus gave no false-negative or false-positive results. Patients undergoing antimalarial therapy were also monitored by the PCR assay. Four of seven patients who were PCR positive for P. vivax at the time of discharge were later readmitted to the hospital with a recurrence of P. vivax infection. We would like to propose that PCR is a sensitive and easy method that can serve as a useful addition to microscopy for the diagnosis and the clinical monitoring of treatment of malaria.     

Usefulness of PCR for Diagnosis of Imported Malaria in Poland

The aim of the present study was to use the polymerase chain reaction (PCR) to detect and identify Plasmodium spp. in diagnostic specimens, especially in those from patients diagnosed by microscopy as having possible mixed infections, and in those demonstrating low parasitemia or those that were parasite-negative. For most of the specimens, the PCR results were in accordance with microscopic findings, and in 16.2% of the cases with low parasitemia PCR enhanced the results by identifying the parasite species. This method detected one additional case of Plasmodium falciparum malaria among the patients with fever of unknown origin. The sensitivity of PCR for detecting Plasmodium DNA was found to correspond to 1.35–0.38 and 0.12 for Plasmodium falciparum and Plasmodium vivax parasites per microliter of blood, respectively. Follow-up examinations demonstrated that most of the patients became negative for Plasmodium DNA from 1 to 4 days after the disappearance of parasitemia, as determined by examination of blood films. In conclusion, PCR performed by the reference laboratory significantly enhanced the microscopic diagnosis of malaria and proved very helpful in cases of low parasitemia and in cases of mixed infection. Electronic Publication     

Evaluation of the OptiMAL Rapid Antigen Test and Species-Specific PCR To Detect Placental Plasmodium falciparum Infection at Delivery

During pregnancy, Plasmodium falciparum infection of the placenta frequently occurs in the absence of parasites in peripheral blood. We investigated the abilities of the OptiMAL rapid immunochromatographic strip test for P. falciparum lactate dehydrogenase and species-specific PCR performed on peripheral blood to detect placental infection or malaria-associated low birth weight. Of 509 Malawian women screened by microscopy, 76 had malaria infection. Among these 509 women, the frequency of peripheral blood parasitemia was low. The OptiMAL test gave positive results in 37 of 171 women tested (one of whom had placental but not peripheral blood parasitemia) and had sensitivities of 71% for peripheral parasitemia and 38% for placental parasitemia compared to the microscopy values. The specificity for peripheral parasitemia was 94%. In 135 women, PCR had sensitivities of 94% for peripheral blood malaria detected by microscopy and 72% for placental infection. In samples examined by PCR, the prevalence of malaria in peripheral blood increased from 26.7% by microscopy to 51.9%. Women with placental malaria and women with malaria in peripheral blood samples by microscopy or OptiMAL testing, but not women with malaria detected only by PCR, had lower-birth-weight babies than did women without malaria by these criteria. Positive results by PCR in the absence of microscopic parasitemia were not associated with low birth weight. Neither OptiMAL nor PCR testing of peripheral blood is adequately sensitive to detect all placental malaria infection, but a positive result by OptiMAL testing identifies women with a high proportion of low-birth-weight babies.     

Diagnostic value of the Binax NOW assay for identifying a pneumococcal etiology in patients with respiratory tract infection.

BACKGROUND AND PURPOSE: Streptococcus pneumoniae is a common pathogen in respiratory tract infections which is usually underestimated with conventional tests, largely due to the fragility of the bacteria. This study assessed the diagnostic value of a rapid test (Binax NOW) for the detection of the pneumococcal antigen in urine. METHODS: Unconcentrated urine samples from 1243 adults and 91 children hospitalized with respiratory tract infections were tested. RESULTS: In all adults with respiratory tract infections, the diagnostic results were as follows: sensitivity, 29 (60%) of 48; specificity, 748 (92.2%) of 811; negative predictive value, 748 (97.5%) of 767; false-positive rate, 63 (68%) of 92. The diagnostic results were similar in adults with lower respiratory tract infections: sensitivity, 21 (64%) of 33; specificity, 658 (92.2%) of 714; negative predictive value, 658 (98.2%) of 670; false-positive rate, 56 (73%) of 77. In children with respiratory tract infections, the diagnostic results were: sensitivity, 4 of 4; specificity 18 (64%) of 28; negative predictive value, 18 of 18; false-positive rate, 10 of 14. The low specificity of the test in children may be due to frequent pneumococcal nasopharyngeal colonization. CONCLUSIONS: High negative predictive values and high false-positive rates were found in both adults and children, indicating that a negative result may be more useful than a positive one in clinical practice. The high specificity of this test in adults indicates its potential value in the choice of initial antibiotic treatment by eliminating pneumococcal infection as a likely cause of respiratory tract infection in a proportion of patients.     

Evaluation of the OptiMAL test for diagnosis of malaria in Venezuela

We evaluated the OptiMAL rapid dipstick test by comparing it with the conventional standard thick-blood film method, for the detection of malaria in two groups of individuals from different Venezuelan endemic areas. One of the groups consisted of individuals with malaria-like symptoms (n = 113) and the other of asymptomatic individuals (n = 89). The classical microscopy analysis of these populations determined that 67.5% were infected with P. vivax, 31.3% with P. falciparum, and 1.2% with mixed infections. The OptiMAL test showed 96.4% sensitivity, 100% specificity, 100% positive predictive value, 97.5% negative predictive value and optimal concordance (kappa = 0.97), capable of detecting any malaria infection in the evaluated population. However, these parameters were lower when the parasitaemia was < or = 300 parasites/microL. Freezing of the samples did not affect the sensitivity and specificity of the test. We concluded that this rapid malaria test is sensitive and specific for rapid diagnosis of malaria in the field and it is a complement to conventional microscopy.     

Evaluation of a Colorimetric PCR-Based Assay To Diagnose Plasmodium falciparum Malaria in Travelers

New diagnostic tests are needed to facilitate the diagnosis of Plasmodium falciparum malaria in the returned traveler. We performed a blinded evaluation of a nonisotopic colorimetric PCR-based assay (Digene SHARP Signal System) and compared the results with those obtained by microscopy and nested PCR for the detection of P. falciparum malaria in 150 febrile travelers. By using nested PCR as the reference standard, the colorimetric assay had a sensitivity of 100% and a specificity of 95.4% for the detection of P. falciparum. This PCR-based nonisotopic assay is a rapid, sensitive, and specific method for the detection of falciparum malaria in returned travelers.