Laboratory Diagnosis of Malaria Infection in Clinically Suspected Cases Using Microscopic Examination, OptiMAL Rapid Antigen Test and PCR

Background: Malaria diagnosis depending on clinical conditions is often unreliable due to the inconsistent signs and symptoms of malaria, leading to over-diagnosis and over-treatment. Correct diagnosis is important for effective management of malaria cases and to reduce w astage of costly drugs. Objective: This study was conducted to detect malaria infection in patients complaining of fever of unknown origin, highly suspected clinically to be due to malaria. OptiMAL rapid antigen test and polymerase chain reaction (PCR) were used in comparison with microscopy. Subjects, Material and Methods: A total of 120 expatriate patients attending King Faisal specialized hospital, Taif, KSA, complaining of fever of unknown origin were screened for malaria parasites by microscopy of Giemsa-stained blood smears, OptiMAL rapid antigen test and genus specific PCR. The diagnostic performance of these methods was statistically compared. Results: Out of 120 clinically suspected cases, 54 (45%) were positive for Plasmodium infection by using microscopy, and of these 45 (83.3%) were infected by P. vivax, 6 (11.1%) by P. falciparum, 1 (1.9%) by P. malariae and 2 (3.7%) were mixed infections (P. vivax and P. falciparum). Correspondingly, OptiMAL test and PCR detected malaria infection in 51(42.5%), and 56(46.7%) patients respectively. The differences in detection rates of these diagnostic tests were not statistically significant ( P>0.05). Using direct microscopy as gold standard, OptiMAL test showed 5 false-positive samples that were negative by microscopy and 8 false-negative samples that were positive by microscopy. At the same time, PCR showed 3 false-positive and one false-negative results. PCR showed a higher sensitivity (98.1%), specificity (95.5%), positive predictive value (94.6%), negative predictive value (98.4%) and diagnostic accuracy (96.6%) than OptiMAL test (85.1%, 92.4%, 90.1%, 88.4%, 89.1%, respectively). Conclusion: Consideration of fever alone as a presumptive prompt diagnosis for anti-malarial treatment would result in huge over-treatment. The use of OptiMAL test and/or PCR assay is a valuable complement to microscopy because these methods help expand the coverage of parasite-based diagnosis and minimize exclusive clinical diagnosis.