Evaluation of Rapid Test in Comparison With Widal Test and Polymerase Chain Reaction For Diagnosis of Typhoid Fever

Abstract

Typhoid fever is a systemic infection caused primarily by S. typhi and is transmitted through the fecal oral route by the consumption of contaminated meat, poultry, eggs and milk. Infection is most common in young children and elderly with peak incidence in summer and fall (rainy season) (Jerrold and Turner, 2010). Diagnosis of enteric fever in an endemic setting is still heavily reliant on clinical presentation and notoriously unreliable tests reiterate the poor sensitivity and specificity of current diagnostics (Parry et al., 2011). The next generation diagnostic point of care test for S. Typhi must be rapid, accurate and affordable in the setting in which it is ultimately destined, and ideally will not rely on expensive equipment, nor highly skilled and trained clinical and laboratory personnel (Andrews et al., 2013). To fulfill the aim of the work, this study was designed to analyze the diagnostic yield, the sensitivity, specificity, accuracy, the cost and the time consuming of Rapid test in comparison with Widal test and polymerase chain reaction for diagnosis of typhoid fever. This study was conducted in co-operation between Tropical Medicine Department, Faculty of Medicine, Ain Shams University and Military Fever Hospital in the period from April 2014 to April 2015. The current study included 30 cases with typhoid disease.All of the studied cases were subjected to the following; full history taking, thorough clinical examination, laboratory investigations, serological tests (Widal test and rapid test) and PCR for diagnosis of typhoid. Regarding the clinical presentations of the studied group; in the present study, all studied patients were presented with fever (100%) the most presenting symptoms beside fever were headache (100%), abdominal pain (100%), sweating (86.7%), diarrhea(73.3%) and vomiting (53.3%). Concerning the laboratory findings of the studied cases; the most common haematological manifestation in our study was anaemia 22/30 (73.3%). Only, 10% of patients had leukopenia, 43.3% patients had an increased level of ALT and 73.3% of patients had an increased level of AST. The clinical picture of typhoid alone cannot always leadtodiagnosis since the symptoms are nonspecific and often atypical;therefore, diagnosisneeds to be supported by laboratory tests.Although many serological tests and new automated blood culturetechniques have been developed to diagnose typhoid, thereare still significant problems in the diagnosis of the disease.Blood cultures are time-consuming, since the average time requiredfor growth has been reported to be 4-7 days. In addition, handlingthe organism poses a high risk of contagion for laboratory personnel. Also, the sensitivity of bloodcultures is 80% during 1st weak and declining 20-30%later in the course of the disease and is affected by antibiotic treatment of the patient. In the current study,we used 30 suspicious blood samples fromMilitary feverhospital with positive Widal test (≥320) for diagnosis of typhoidby PCR and Rapid test. In our series,thirty samples had positive Widal test, 25 had positive Rapid test and 21 samples had positive PCR for typhoid. The sensitivity, specificity and accuracy of Rapid test were 100%, 55.6% and 86.7%, respectively. So, Rapid test has better characteristics than Widal test; both had perfect sensitivity but Rapid test had higher specificity and diagnostic accuracy. In the current study, we considered PCR is the referencefor diagnosis of typhoid. As the PCR method is more sensitive and specific than culture and serology for diagnosis of typhoid from peripheral blood in suspected cases. So the current series revealed that Rapid test was fast and cheap test. Widal test was the cheapest test, and faster than PCR. This may makeRapid test to be suitable for national serological surveys, and laboratories with large diagnostic workloads.