Evaluation of Diagnos Malaria Stix test (antigen detection assay) for diagnosis of malaria

Malaria is one of the most common parasitic infection in India. The diagnosis largely depends on peripheral blood smear examination. Newer diagnostic methods like various antigen detection assays are now in use for prompt diagnosis and treatment. This study was done to determine the effectiveness of Diagnos Malaria Stix (antigen detection) assay in diagnosis of malaria. This involves detection of PfHRP-2 antigen and P.V. specific pLDH antigen. 162 patients with signs and symptoms of malaria included in the study. Leishman stained blood smear examination was done for all patients. Commercially available Diagnos Malaria Stix assay was used. Diagnos Malaria Stix showed sensitivity, specificity positive and negative predictive values of 100% each while Sensitivity, specificity, positive and negative predictive values of Leishman stained blood smear examination were 45.45%, 100%, 100% and 92% respectively.     

Field trial of the RTM dipstick method for the rapid diagnosis of malaria based on the detection of Plasmodium falciparum HRP-2 antigen in whole blood

The performance of the Quorum RapidTest Malaria (RTM) dipstick method that detects Plasmodium falciparum histidine-rich protein-2 (PfHRP-2) antigen in whole blood was evaluated in a malaria endemic area. Results were compared with conventional Giemsa-stained blood films. Of 306 people tested 37.9% (116/306) were found to be parasitaemic; of these 66.4% (77/116) were P. vivax and 32.8% (38/116) were P. falciparum infections. There was only one (0.9%) mixed P. falciparum plus P. vivax infection.The RTM test was positive in 35/36 patients with P. falciparum identified on blood smear examination, resulting in a sensitivity of 97.2% [95% confidence interval (CI): 91.6-102.8%]. Specificity was 96.3% (95% CI: 93.9-98.6%).The RTM test had a positive predictive value of 77.8% (95% CI: 65.7-89.9%) and a negative predictive value of 99.6% (95% CI: 98.4-100.8%). Of the 10 false positives, seven reported recent malaria episode and treatment, indicating persistence of antigenaemia. If these were assumed truly infected, the positive predictive value is increased to 93.3% (95% CI: 85.8-100.8%).The RTM test was positive in all seven P. falciparum infections with gametocytes and one mixed infection, but was negative in all falciparum gametocytes and relapsing fever cases. All but one P. vivax infection gave negative result on the RTM test.The RTM test missed one patient with parasitaemia. The test is highly sensitive and specific requiring no instrument or trained personnel. It appears to be a very useful tool for rapid diagnosis of malaria, especially in the rural health institutions with limited diagnostic facilities.     

Urban malaria in the Sahel: prevalence and seasonality of presumptive malaria and parasitaemia at primary care level in Chad

ObJECTIVE: To assess malaria prevalence rates and seasonal patterns among clinically diagnosed malaria cases at the level of primary care facilities in an urban Sahelian setting. METHOD: Screening all patients consulting two private and two governmental providers on a randomly selected weekday over a period of 9 months. Patients with presumptive malaria underwent a blood test. RESULTS: Of 1658 patients included in the survey, 47% were clinically diagnosed and treated as malaria cases. Malaria was more often diagnosed by private providers. There were no clear seasonal patterns in presumptive malaria. A 30% of clinically diagnosed cases were positive for Plasmodium (all falciparum) by thick film examination. Thus, false positive cases constituted more than 70% of the clinically diagnosed malaria cases. The highest positive prevalence rates were found at the end and shortly after the rainy season (44%-47%) and the lowest during the dry season (2%). CONCLUSIONS: Clinical diagnosis of malaria has a very low positive predicted value in this low endemicity urban setting, and its low specificity leads to inappropriate care for a large proportion of patients. This has a major impact on economic costs for health services and households. In the Sahel, systematic use of microscopy-based diagnosis and/or rapid diagnostic tests should be considered to appropriately manage malaria and non-malaria cases.     

Microscopy and outpatient malaria case management among older children and adults in Kenya

OBJECTIVE: To evaluate the accuracy of routine malaria microscopy, and appropriate use and interpretation of malaria slides under operational conditions in Kenya. METHODS: Cross-sectional survey, using a range of quality of care assessment tools, at government facilities with malaria microscopy in two Kenyan districts of different intensity of malaria transmission. All patients older than 5 years presenting to outpatient departments were enrolled. Two expert microscopists assessed the accuracy of the routine malaria slide results. RESULTS: We analysed 359 consultations performed by 31 clinicians at 17 facilities. Clinical assessment was suboptimal. Blood slide microscopy was performed for 72.7% of patients, who represented 78.5% of febrile patients and 51.3% of afebrile patients. About 95.5% of patients with a positive malaria microscopy result and 79.3% of patients with a negative result received antimalarial treatment. Sulphadoxine-pyremethamine monotherapy was more commonly prescribed for patients with a negative test result (60.7%) than for patients with a positive result (32.4%). Conversely, amodiaquine or quinine were prescribed for only 14.7% of patients with a negative malaria microscopy result compared to 57.7% of patients with a positive result. The prevalence of confirmed malaria was low in both high (10.0%) and low-(16.3%) transmission settings. Combining data from both settings, the sensitivity of routine microscopy was 68.6%; its specificity, 61.5%; its positive predictive value, 21.6% and its negative predictive value, 92.7%. CONCLUSIONS: The potential benefits of microscopy are currently not realised because of the poor quality of routine testing and irrational clinical practices. Ambiguous clinical guidelines permitting treatment of older children and adults with a negative blood slide also undermine rational use of antimalarial drugs.     

Post-arrival screening for malaria in asymptomatic refugees using real-time PCR

Malaria is a significant health risk to refugee populations originating from endemic areas, but there is little consensus on screening and/or treatment approaches for malaria in this population. Furthermore, detection of malaria in semi-immune asymptomatic refugees is limited by the sensitivity of diagnostic tests used for screening. We determined the prevalence of malaria by microscopy and real-time polymerase chain reaction (PCR) in a consecutive population of 324 asymptomatic refugees examined in Edmonton, Canada, during 2009-2010. Although all thick and thin blood smear results were negative, 10 subjects (3.1%) tested PCR positive for Plasmodium DNA. Interestingly, 6 of 10 PCR positive subjects are at risk of malaria relapse by P. vivax or P. ovale infections. These results suggest that appropriate guidelines for malaria screening should consider the risk of relapsing infections, and they highlight the potential usefulness of real-time PCR in the diagnosis of asymptomatic malaria.     

A retrospective review of malaria cases seen in a non-endemic area of South Africa

BACKGROUND: Malaria is a risk for travelers to endemic areas. We describe the diagnosis and treatment of malaria in Pretoria, a non-endemic area in South Africa. METHODS: Records of specimens submitted to the medical microbiology laboratory for malaria investigations over 3 years were reviewed with follow up of hospital records for positive specimens for clinical data. The laboratory performs malaria smears and uses HRP2-Ag testing for rapid diagnosis of Plasmodium falciparum. RESULTS: A total of 516 specimens were received, with a 211/516 (41%) malaria smear positive rate. The number of malaria positive specimens has been increasing overtime and this increase was statistically significant in children [p=0.005]. HRP2-Ag testing was done on 430 specimens with124/430 (29%) being positive, of which 10/124 (8%) were smear negative, giving 98% sensitivity. Hospital records for 198/211 (94%) smear positive cases showed that 190/198 (96%) of the patients had a travel history with 170/190 (71%) having traveled to Mozambique, a malaria endemic country. Most patients presented with uncomplicated malaria; the CFR was 4/198 (2%). Treatment mainly followed South African national guidelines. CONCLUSION: Imported malaria is increasingly being diagnosed in returning travelers, especially from Mozambique. Rapid antigen tests remain useful for the diagnosis of malaria in non-endemic areas.     

Utility of a Point-of-Care Malaria Rapid Diagnostic Test for Excluding Malaria as the Cause of Fever among HIV-Positive Adults in Rural Rakai, Uganda

We compared results of a malaria rapid diagnostic test (Binax Now^® Malaria, Binax-M, Inverness Medical Innovations, Inc., Waltham, MA) performed at rural mobile clinics in Uganda by clinicians evaluating febrile adult HIV patients to thick smear evaluated at a central laboratory by trained microscopists. Two hundred forty-six samples were analyzed, including 14 (5.7%) which were thick-smear positive for falciparum malaria. Sensitivity of Binax-M compared with thick smear was 85.7% (95% CI: 57.2–98.2), specificity 97.8% (95% CI: 94.9–99.3), positive and negative predictive values were 70.6% (95% CI: 44.0–89.7) and 99.1% (95% CI: 96.8–99.9), respectively. The rapid diagnostic test accurately ruled malaria “in or out” at the point-of-care, facilitating appropriate clinical management and averting unnecessary anti-malarial therapy.     

Comparison of different diagnostic techniques in Plasmodium falciparum cerebral malaria

BACKGROUND & OBJECTIVES: Plasmodium falciparum cerebral malaria remains a major health problem in India. The efficacy of treatment of cerebral malaria lies in its early diagnosis through rapid diagnostic methods. ParaSights-F test detects HRP-2 antigen secreted by parasitised red blood cells and quantitative buffy coat assay (QBC) is examination of buffy coat for the presence of malarial parasite stained with acridine orange. This study was performed to evaluate the effectiveness of ParaSight-F test and QBC assay as diagnostic methods in the patients of cerebral malaria. METHODS: Fifty clinically diagnosed patients of cerebral malaria were included in the study. ParaSight-F test, QBC and conventional blood smear examination was done. Patients who were in coma and there were no obvious features of bacterial or viral etiology were investigated for cerebral malaria by these diagnostic methods. RESULTS: ParaSight-F test, QBC and peripheral blood smears were examined. Patients were followed-up for signs of clinical recovery. ParaSight-F test was positive in 47 patients, QBC in 46 while blood smear examination was positive in 28 cases. INTERPRETATION & CONCLUSION: Sensitivity and specificity of ParaSight-F test were found to be 96.6 and 94% while QBC showed 97.8 and 100% respectively. ParaSight-F test and QBC were found to be novel methods for diagnosis of cerebral malaria especially in the cases where diagnosis can not be made by conventional blood smear examination due to low parasitaemia. These rapid diagnostic methods help in early therapeutic intervention.     

Predictive factors of malaria in travelers to areas where malaria is endemic

BACKGROUND: The differentiation of malaria from other causes of fever is difficult. The development of tools for rapid and specific clinical diagnosis is of paramount importance for the identification of individuals infected with malaria. METHOD: A 4-year prospective study to identify the clinical and biological variables associated with malaria included all patients suspected of having malaria who presented in the emergency department (ED) of a French hospital. RESULTS: Of 783 patients admitted to the ED with suspected malaria, 145 had positive findings of a thick smear for Plasmodium species, mainly Plasmodium falciparum (90.3%). In univariate analysis, the following 12 variables were significantly associated with diagnosis of malaria: older than 30 years, male sex, immigration to France from an area where malaria is endemic, a visit to sub-Saharan Africa, insufficient antimalaria prophylaxis, fever, chills, absence of diarrhea, a leukocyte count within the reference range, thrombocytopenia, and increased lactate dehydrogenase and bilirubin levels. In multivariate analysis, the factors predictive of malaria included a visit to sub-Saharan Africa (odds ratio [OR], 7.7; 95% confidence interval [CI], 2.8-21.3), a temperature of at least 38.5 degrees C (OR, 6.2; 95% CI, 2.8-13.3), chills (OR, 3.0; 95% CI, 1.4-6.6), thrombocytopenia (OR, 16.5; 95% CI, 7.1-38.3), and abnormally high total bilirubin levels (OR, 21.5; 95% CI, 6.4-72.5). However, alone or combined, these features had insufficient sensitivity (95.0%) and low specificity (55.0%) for the diagnosis of malaria. CONCLUSIONS: Malaria should be suspected in all patients presenting with complaints after travel to an area where malaria is endemic, and these patients should undergo blood microscopy.     

Clinical diagnosis of malaria: can we improve?

Most cases of malaria in Zimbabwe are diagnosed on the basis of clinical suspicion, without laboratory tests. Of patients treated, between 10 and 30% have malaria parasites on blood slide examination. Can diagnosis be improved by a systematic history? We examined this question in 287 patients treated for malaria in an area of year-round transmission in Zimbabwe. The most common complaints were 'headache' (85.7%), 'bodily weakness' (79.0%) and 'fever/feeling hot' (73.2%). Eighty patients (28%) had malaria parasites on blood smear. Using the blood slide as the standard, we calculated the sensitivity, specificity and positive predictive value of a variety of clinical symptoms and signs. None had a positive predictive value substantially higher than the unknown diagnostic criteria used by health workers (28%). Multivariate analysis showed that 15 different demographic and clinical variables did not significantly predict a positive blood slide result. We conclude that, in this setting, clinical history alone will not improve the diagnosis of malaria.     

Evaluation of the performance of CareStart™ Malaria Pf/Pv Combo and Paracheck Pf tests for the diagnosis of malaria in Wondo Genet, southern Ethiopia

Objective

To evaluate the diagnostic performance of CareStart™ Malaria Pf/Pv Combo test relative to microscopy for the diagnosis of falciparum and vivax malaria in Ethiopia.

Methods

668 febrile patients visiting two health centers in Wondo Genet, southern Ethiopia, involved in this study in 2008. Giemsa-stained thin and thick blood smears were prepared and microscopically examined under a 100× oil immersion microscope objective for Plasmodium species identification and determination of parasitaemia, respectively. CareStart™ Malaria Pf/Pv Combo test and Paracheck Pf^® test were performed as per the manufacturers’ instruction.

Findings

The diagnostic validity of CareStart™ Malaria Pf/Pv Combo test for the diagnosis of Plasmodium falciparum were very good with sensitivity of 99.4%, specificity of 98%, positive predictive value of 94.4% and negative predictive value of 99.8%. Sensitivity, specificity, positive predictive value and negative predictive value of the test for the diagnosis of P. vivax were 99.4%, 98.2%, 94.5% and 99.8%, respectively. The diagnostic performance of CareStart™ Malaria Pf/Pv Combo test is comparable to that of Paracheck Pf^® test for the diagnosis of P. falciparum (sensitivity 99.4%, specificity 98.2%).

Conclusion

Although CareStart™ Malaria Pf/Pv Combo test and Paracheck Pf^® test have comparable diagnostic performance for the diagnosis of P. falciparum, CareStart™ Malaria Pf/Pv Combo test has the added advantage of diagnosing P. vivax. Hence, it is preferable to use CareStart™ Malaria Pf/Pv Combo test for the diagnosis of malaria in areas where microscopy is not accessible and where malaria due to P. falciparum and P. vivax are co-endemic as in Ethiopia.     

Clearance kinetics of parasites and pigment-containing leukocytes in severe malaria

In tropical areas, where unsupervised use of antimalarial drugs is common, patients with an illness consistent clinically with severe malaria but with negative blood smears pose a management dilemma. Malaria pigment is evident in peripheral blood leukocytes in greater than 90% of patients with severe malaria. To characterize the clearance kinetics of parasitized erythrocytes and malaria pigment-containing leukocytes, sequential peripheral blood and intradermal smears were assessed in 27 adult Vietnamese patients with severe falciparum malaria. The clearance of parasitized erythrocytes and pigment- containing monocytes (PCMs) followed first order kinetics. The elimination of pigment-containing neutrophils (PCNs) was first order initially, but deviated from this when counts were low. Clearance of peripheral blood PCMs (median clearance time, 216 hours; range, 84 to 492 hours) was significantly slower than that of parasitized erythrocytes (median, 96 hours; range, 36 to 168 hours) or PCNs (median, 72 hours; range, 0 to 168 hours; P < .0001). Intradermal PCM clearance times were the longest of all (median, 12 days; range, 6 to 23 days; significantly longer than peripheral blood PCM clearance, P < .001). Twenty-one (88%) patients still had signs, symptoms, or laboratory features of severe malaria after parasite clearance but before phagocyte pigment clearance. Sixteen of the 23 surviving patients (70%; 95% confidence interval, 50% to 87%) still had intraleukocytic malaria pigment on peripheral blood films 72 hours after parasite clearance. Thus, by determining the distribution of malaria pigment in peripheral blood and intradermal phagocytes, the time since effective antimalarial treatment started can be estimated. Microscopy for intraleukocytic pigment is valuable in the differential diagnosis of severe febrile illnesses in malarious areas where uncontrolled use of antimalarial drugs is widespread.     

Severe anaemia in Zambian children with Plasmodium falciparum malaria

BACKGROUND: Severe anaemia and cerebral malaria are highly prevalent complications of Plasmodium falciparum malaria among African children. The mechanisms of severe malarial anaemia, and the relative importance of this condition in comparison to cerebral malaria, are not known for many regions of Africa. METHODS We reviewed the records of 6200 children up to 6 years of age admitted to one rural Zambian hospital between 1994 and 1996. Severe malarial anaemia was defined as an haemoglobin concentration < 5.0 g/dl in a patient with asexual forms of P. falciparum in the peripheral blood. Cerebral malaria was defined as impaired consciousness (Blantyre coma score < 5) not attributable to any other cause in a patient with a positive malaria smear. RESULTS Severe malarial anaemia was found in 590 children (9.5% of paediatric admissions) and strictly defined cerebral malaria occurred in 286 children (4.6% of paediatric admissions); 98 of these patients had the combination of both complications. Severe malarial anaemia correlated strongly with the degree of parasitaemia, with malnutrition as indicated by low weight for age, with absence of fever and with presentation late in the malaria season. In comparison, patients with cerebral malaria were more often febrile and presented earlier in the malaria season. The case fatality rate of severe malarial anaemia (0.088) was about half that of cerebral malaria (0.189), but because severe malarial anaemia was more common, these two forms of complicated malaria were implicated in similar numbers of in-hospital paediatric deaths. CONCLUSION Severe anaemia is a more common complication of P. falciparum malaria in hospitalized Zambian children than cerebral malaria and is associated with a similar number of deaths. Malnutrition and changes in immune response patterns due to prolonged exposure to P. falciparum may contribute to the development of this complication.     

Spontaneous subdural empyema in falciparum malaria: a case study

CLINICAL HISTORY: Malaria is one of the most common diseases in the tropical countries. Cerebral malaria is usually a diffuse symmetric encephalopathy with focal signs being unusual. METHODS : We present a three-year old girl lapsing into unconsciousness following a seizure while undergoing treatment for malaria. Imaging revealed a large heterogenous density, left hemispheric acute subdural haematoma with brain herniation. Investigations revealed anaemia, thrombocytopenia and positive peripheral blood smear for falciparum malaria. RESULTS: Treatment involved surgical evacuation of the clot and the associated subdural empyema, intravenous quinine and antibiotics. CONCLUSION: This is the second case report of spontaneous subdural empyema in complicated falciparum malaria and highlights a rare but surgically manageable complication.     

Epidemiologic tools for malaria surveillance in an urban setting of low endemicity along the Colombian Pacific coast

An evaluation of 3 different methods for malaria diagnosis was carried out in an urban area of low endemicity on the Pacific coast of Colombia. Samples were collected from 833 symptomatic patients at a malaria clinic and examined by the polymerase chain reaction (PCR), quantitative buffy coat (QBC; Becton Dickinson, Franklin Lakes, NJ) method, and the traditional thick blood smear. The prevalence of Plasmodium falciparum malaria was 5.88% by thick blood smear, 7.34% by the QBC method, and 21.87% by PCR. The agreement between microscopists was 99.5%. The agreement between the QBC method and thick blood smear was 96.13% (n = 745). Samples positive by PCR but negative by thick blood smear or conversely negative by PCR and positive by thick blood smear were usually of low-level parasitemias. All 3 methods showed agreement in 76.3% of the samples. Sixty-nine (18.8%) samples were positive by PCR but negative by the other 2 methods. Ten samples were positive by both the QBC method and thick blood smear but negative by PCR; most of them had low-level parasitemias. The use of malaria diagnostic methods for epidemiologic surveillance is discussed.     

Performance of the OptiMAL test for malaria diagnosis among suspected malaria patients at the rural health centers

The OptiMAL test detects both Plasmodium falciparum and P. vivax malaria infections. In this study, we evaluated the performance of the OptiMAL test at the Basic Health Units (BHUs) and the District Health Quarter (DHQ) Center in rural villages of Punjab, Pakistan that provide minimal health services. Two sets of blood specimens obtained from 930 suspected malaria patients attending these BHUs were tested at BHUs and the DHQ Center by microscopy and the OptiMAL test. At the BHUs, 231 (25%) of the patients were positive by microscopy and 278 (30%) patients tested positive by the OptiMAL test. At the DHQ Center, microscopic analysis of a second set of specimens from the same patients confirmed the malaria infection in 386 (42%) patients and the OptiMAL test result was positive in 300 (32%) patients. To determine the performance of OptiMAL test at the BHUs and the DHQ Center, all data were compared with microscopy results obtained at the DHQ Center. The OptiMAL test results for P. falciparum at the BHUs were comparable to those of the OptiMAL test at the DHQ Center. However, the sensitivity, positive predictive value (PPV), and negative predictive value (NPV) of the OptiMAL test were considerably lower for P. vivax infections than for P. falciparum infections, irrespective of whether the test was performed at the BHUs or at the DHQ Center (P. falciparum: sensitivity = 78-85%, PPV = 89-97%, NPV = 96-98%; P. vivax: sensitivity = 61-76%, PPV = 88-95%, NPV = 90-93%). The OptiMAL test also detected a number of false-positive and false-negative results at both the BHUs and the DHQ Center. The false-positive results ranged from 1% to 2%; however, the number of false-negative results was much higher (BHUs: P. falciparum = 22%, P. vivax = 39%; DHQ Center: P. falciparum = 15%, P. vivax = 24%). In conclusion, these results, when combined with other advantages of the OptiMAL test, suggest that this test can be used by relatively inexperienced persons to diagnose malaria infection in rural areas where facilities for microscopy are not available.     

广西疟疾流行现状及消除疟疾可行性分析

目的 分析广西壮族自治区（广西）当前疟疾流行现况和趋势,探讨广西2018年实现消除疟疾目标的可行性。方法收集2001-2011年广西本地发热患者、疟疾病灶点居民和流动人口等疟疾监测资料,采用流行病学方法,对全区疟疾发病情况、病例的分布与分类等进行描述和统计分析。结果 2001-2011年,广西共血检本地发热患者491.63万人次、病灶点居民19.59万人次、外出回归人员28.25万人次、外来人群22.83万人次,共检出疟疾患者1 896例,4类人群平均血检阳性率分别为0.004 8%、0.007 7%、0.480％和0.127％。本地感染病例从2001年的51例下降到2009年的1例,2010-2011年未发现本地感染病例和输入性继发病例。全区疟疾发病率控制在1/10万以下,疟疾患者以输入性病例为主。结论 对照世界卫生组织消除疟疾的标准,广西已进入消除疟疾阶段巩固期。只要政府和相关部门继续加强对全区劳务输出等归国人员监测和管理,同时采取有效的防控措施,广西于2018年达到消除疟疾的目标是可以实现的。     

Effects of revised diagnostic recommendations on malaria treatment practices across age groups in Kenya

Objective The recent change of treatment policy for uncomplicated malaria from sulfadoxine‐pyrime‐thamine to artemether‐lumefantrine (AL) in Kenya was accompanied by revised malaria diagnosis recommendations promoting presumptive antimalarial treatment in young children and parasitological diagnosis in patients 5 years and older. We evaluated the impact of these age‐specific recommendations on routine malaria treatment practices 4–6 months after AL treatment was implemented. Methods Cross‐sectional, cluster sample survey using quality‐of‐care assessment methods in all government facilities in four Kenyan districts. Analysis was restricted to the 64 facilities with malaria diagnostics and AL available on the survey day. Main outcome measures were antimalarial treatment practices for febrile patients stratified by age, use of malaria diagnostic tests, and test result. Results Treatment practices for 706 febrile patients (401 young children and 305 patients ≥5 years) were evaluated. 43.0% of patients ≥5 years and 25.9% of children underwent parasitological malaria testing (87% by microscopy). AL was prescribed for 79.7% of patients ≥5 years with positive test results, for 9.7% with negative results and for 10.9% without a test. 84.6% of children with positive tests, 19.2% with negative tests, and 21.6% without tests were treated with AL. At least one antimalarial drug was prescribed for 75.0% of children and for 61.3% of patients ≥5 years with a negative test result. Conclusions Despite different recommendations for patients below and above 5 years of age, malaria diagnosis and treatment practices were similar in the two age groups. Parasitological diagnosis was under‐used in older children and adults, and young children were still tested. Use of AL was low overall and alternative antimalarials were commonly prescribed; but AL prescribing largely followed the results of malaria tests. Malaria diagnosis recommendations differing between age groups appear complex to implement; further strengthening of diagnosis and treatment practices under AL policy is required.     

Field evaluation of the ICT Malaria Pf/Pv immunochromatographic test for the detection of asymptomatic malaria in a Plasmodium falciparum/vivax endemic area in Thailand

Rapid antigen assays provide an effective tool for the detection of malaria in symptomatic patients. However, the efficacy of these devices for detecting asymptomatic malaria, where parasite levels are normally significantly lower than in symptomatic patients, is less well established. We evaluated the efficacy of a new combined Plasmodium falciparum-Plasmodim vivax immunochromatographic test (ICT Malaria Pf/Pv) in a cross-sectional malaria survey of the village of Ban Kong Mong Tha, Kanchanaburi Provice, Thailand, from August to December 2000. A total of 1,976 bleeds were made from 559 individuals over the course of the study. Blinded microscopy of thick and thin blood films was used as the gold standard; all discordant and 10% of concordant results were cross-checked. Of 1,976 ICT Malaria Pf/Pv dipsticks tested, 98.3% (n = 1,943) performed as expected, as evidenced by the appearance of the control line. The ICT Malaria Pf/Pv test was both sensitive (100.0%) and specific (99.7 %) for the diagnosis of falciparum malaria with parasitemias of > or = 500 trophozoites/microL; however, only 15.9% (13/82) of infected individuals had parasitemia rates this high. When P. falciparum parasitemia rates were < 500/microL, the sensitivity of the diagnosis was only 23.3%, with a positive predictive value (PPV) and a negative predictive value (NPV) of 76.2 and 97.2%, respectively. The ICT Malaria Pf/Pv test was specific, but not sensitive, for the diagnosis of vivax malaria with parasite rates of > or = 500 trophozoites/microl, with sensitivity, specificity, PPV, and NPV of 66.7%, 99.9%, 66.7%, and 99.9%, respectively. At parasite rates of < 500/microL, corresponding values were 0.0%, 99.9%, 0%, and 95.1%. Because of the relatively high cost of these assays, low parasite rates found in the majority of asymptomatic individuals, and low sensitivity of this assay with rates of < 500/microl, use of this assay as a tool for active case detection is of limited value in western Thailand.