This study compares the performance of clinical diagnosis and three laboratory diagnostic methods (thick film microscopy (TFM), rapid diagnostic test (RDT), and polymerase chain reaction (PCR)) for the diagnosis of
Malaria remains an important public health concern in countries where transmission occurs regularly as well as in areas where transmission has been largely controlled or eliminated. It was estimated that there are 39 million children under 5 years of age who experience 33.7 million malaria episodes and 152,000 childhood deaths from malaria each year in areas suitable for seasonal malaria chemoprevention [
In most endemic countries malaria diagnosis depends mainly on clinical evidence and in some cases thick film microscopy (TFM) and rapid diagnostic technique (RDT) may be used for laboratory confirmation. Microscopy remains the gold standard for malaria diagnosis and it is less costly with a threshold sensitivity of 5 to 50 parasite/
Clinical diagnosis is imprecise but remains the basis for therapeutic care for the majority of febrile patients in malaria endemic areas, where laboratory support is often out of reach. Clinical diagnosis also referred to as presumptive diagnosis is the least expensive and most commonly used method and is the basis for self-treatment in endemic countries. Overlap of malaria symptoms with other tropical diseases like typhoid fever, respiratory tract infections and viral infections impairs the specificity of presumptive diagnosis thereby encouraging indiscriminate use of antimalarials in endemic areas. Accuracy of clinical diagnosis varies with the level of endemicity, malaria season, and age group. Therefore no single clinical algorithm can be regarded as a universal predictor [
This paper reports the comparative performance of clinical diagnosis, TFM, RDT, and PCR in the diagnosis of
The study was carried out in Osogbo located in the Western part of Nigeria. Osogbo is the state capital of Osun State, Nigeria, and it represents a typical urban setting in Nigeria. Malaria is present throughout the year with a marked increase during the raining season. Patients (ages 4 months to 20 years) who were clinically diagnosed for malaria at the outpatient departments of General Hospital Asubiaro and LAUTECH Health Centre in Osogbo were recruited into the study. Exclusion criteria used were complete absence of malaria symptoms and unwillingness to participate. All the patients that were clinically diagnosed were subsequently confirmed using TFM, RDT, and PCR before treatment. Ethical approval was obtained from the ethical committee of Osun State Hospital Management Board, Osogbo.
Clinical diagnosis based on fever (temperature ≥ 37.5°C) and/or history of fever was carried out by physicians at the outpatient departments of the hospitals. Other symptoms considered for clinical diagnosis include headache, joint pains, body weakness, cough, diarrhea, loss of appetite/refusal of feeds, abdominal pain, and generalized body weakness.
5 mL of blood was collected aseptically from antecubital vein of consenting febrile patients, into EDTA bottle. RDT was performed on about 5
10
Data obtained was analyzed using SPSS package version 16.0. The sensitivity, specificity, and predictive values of each of the three test methods were calculated by comparing to a composite reference gold standard generated from the three methods. The composite reference method was defined as a method that is positive for malaria parasites by all the three methods (TFM, RDT, and PCR) and also negative for malaria parasites by all the three methods. This gives the method 100% hypothetical sensitivity, specificity, and positive and negative predictive values. The sensitivity, specificity, and predictive values of each of the 3 methods were then calculated using the formulas
We compared the diagnostic value of 3 methods (TFM, RDT, and PCR) for the detection of malaria parasites in Nigeria. A total of 217 individuals clinically diagnosed for malaria were recruited into the study. Of these, 103 were males and 114 were with a male to female ratio of 0.9. The mean age of the patients was 8 years ± 3.04 and the mean axillary temperature was 38.2°C ± 0.96. The general characteristics of the patients are shown in Table
Characteristics of study subjects and prevalence of malaria based on different diagnostic methods.
Number of subjects | 217 |
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Mean age (years) | 8 years ± 3.04 |
Sex male/female | 103/114 |
Mean temperature °C | 38.2°C (±0.96) |
No. positive by microscopy (%), MPD ± SD | 106 (48.8%), |
No. positive by RDT (%) | 84 (38.7%) |
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No. positive by stevor PCR (%) | 125 (57.6%) |
MPD: mean parasite density by microscopy.
Microscopy versus RDT versus PCR =
Using a composite reference (gold standard) method generated from the three diagnostic methods, only 71 (32.7%) patients were found to be truly infected, with
Sensitivity, specificity, and predictive values of the three diagnostic methods.
Diagnostic methods | Parameter for assessment | |||||||
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TP |
FP |
TN |
FN |
Sensitivity (%) | Specificity (%) | PPV (%) | NPV (%) | |
TFM | 71 | 35 | 90 | 21 | 77.2 | 72 | 67 | 81.1 |
RDT | 71 | 13 | 90 | 43 | 62.3 | 87.4 | 84.5 | 67.7 |
PCR | 71 | 54 | 90 | 2 | 97.3 | 62.5 | 56.8 | 97.8 |
Composite reference | 71 | 0 | 90 | 0 | 100 | 100 | 100 | 100 |
TP: true positive; FP: false positive; TN: true negative; FN: false negative; TFM: thick film microscopy;
RDT: rapid diagnostic test; PCR: polymerase chain reaction; no: number; %: percent.
Correlation of RDT and PCR to parasite density observed by microscopy is shown in Table
Stratification by parasite density in thick blood smear and correlation with rapid diagnostic test (RDT) and stevor PCR.
Parasite count range | ||||
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0 | 1–100 | 101–1000 |
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No. observed | 109 | 10 | 81 |
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Mean parasite count/µL (range) | 0 | 91 (41.6–100) | 408 (110–948) |
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No. positive for clinical | 109 (100%) | 10 (100%) | 81 (100%) |
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No. negative for clinical | 0 | 0 | 0 |
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No. positive for RDT | 22 (20.2%) | 2 (20.0%) | 47 (58.0%) |
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No. negative for RDT | 87 (79.8%) | 8 (80.0%) | 34 (42.0%) |
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No. positive for PCR | 29 (26.6%) | 8 (80.0%) | 73 (90.1%) |
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No. negative for PCR |
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This study provides a dataset for judging the performance of clinical diagnosis against TFM, RDT, and PCR for the detection of
Our results show that the continuous practice of using clinical diagnosis as the basis for antimalarial treatment in endemic area is by far not an effective diagnostic method in our study area. Out of the 217 (100%) patients that were clinically diagnosed for malaria, 104 (49.8%), 83 (38.2%), and 123 (56.7%) were positive by TFM, RDT, and PCR, respectively. Invariably irrespective of the laboratory method, about half of the patients who were diagnosed as having malaria through clinical diagnosis (syndrome approach) and who should have received antimalarial turned out to be parasite-negative. There is therefore an urgent need to review the clinical diagnosis procedure. Although it may be argued that in some cases especially in children, promptness of malaria treatments reduces the progression of simple malaria to severe malaria, which still encourages syndromic approach to malaria diagnosis. Nevertheless malaria over diagnosis is still a major public health problem in Africa with studies suggesting between 50% and 99% of those prescribed antimalarial to be test negatives depending on endemicity of the clinical setting [
In this study routine microscopic examination of Giemsa-stained blood smears which is considered as the gold standard for malaria diagnosis had a sensitivity of 77.2% and was able to detect more parasites than the RDT (sensitivity 62.3%). Though the specificity of microscopy (72%) was not as high as that of RDT (87.4%); nevertheless, it has high sensitivity, possibility for quantification of parasitemia, and easy handling which is a good advantage. Detection of parasites depends on many factors including the amount of blood processed and the competence of the microscopist, among others [
Different PCR based methods have been constantly shown to be powerful tools for malaria diagnosis with better sensitivity than conventional microscopy and antigen-based diagnostic tests [
Greater percentage of children presented at general outpatient department of the hospital in our study with fever were diagnosed for malaria (PCR—56.7%, microscopy 49.8%, and RDT 38.2%). Available records also show that at least 50% of the population of Nigeria suffer from at least one episode of malaria each year accounting for over 45% of all out-patient visits [
In conclusion our study revealed the need for complete shift from symptom-based diagnosis to parasite-based diagnosis. This can bring significant improvement to tropical fever management and reduce drug wastage and also help to curtail development of malaria drug resistance.
The authors have no conflict of interests to declare.
The authors are grateful to Mr. Akeem Abiodun and Mr. Adeola Ayileka for their technical support. Sincere appreciation also goes to all consenting participants and parents of participants for their cooperation.