Asif Naveed, Shabnam Bashir, Romaisa Naeem.
False Positivity of Widal Test in Malaria.
Pak J Med Health Sci Jan ;12(2):437-39.

Background: Malaria is endemic in Pakistan. Malaria generally affects One billion people each year. Malaria has a mortality rate of 1–3 million out of the one billion affected . Malaria is a mosquito-borne infectious disease and it is caused by 5 species of Plasmodium. Typhoid fever is caused by Salmonella typhi. The Widal test was developed by F Widal in 1896 for the purpose of aiding the diagnosis of typhoid fever. It utilises a suspension of killed Salmonella typhi as antigen, to detect typhoid fever in the suspected Salmonella typhi infected patients presenting with fever. Cross reactions are seen when antibody produced by non-typhoidal antigens reacts with typhoid antigen causing false positive results . False interpretation of the test results may lead to misdiagnosis and mismanagement of the patient, causing high morbidity and mortality as the treatment formalaria and typhoid are altogether different. Aim: To assess frequency of false positivity of widal test in malarial patients. Study design: Case series. Study period and settings: June 2014 – February 2015 at King Edward Medical University / Mayo hospital Lahore Methods: The study was conducted at King Edward Medical University / Mayo Hospital LHR. All the patients who have peripheral smear positive formalarial parasite were enrolled in the study. Peripheral Smear of the patients having positive malarial parasite were reviewed and type of malarial parasite identified. Widal test, blood culture, urine and faeces culture were done . Result: Among the 75 patients having malarial parasite on peripheral smear 10 (13.3%) had Widal test positive. Blood culture for Salmonella typhi was positive in only one (1.3%) of the 10 having widal positive. Conclusion: Investigation to rule in/rule out malaria shall always be done in patients presenting with PUO malaria and the use of the Widal test alone for the diagnose of typhoid fever should be limited to situations where no other confirmatory supportive test, such as positive culture, is available. Due to this many cases of pyrexia of unknown origin (PUO) receive the management of typhoid fever, based upon a false-positive Widal test thus resulting in under diagnosis of malaria.

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