USE OF PCR FOR DETECTION OF SALMONELLA FROM SUSPECTED CASES OF TYPHOID FEVER

Abstract

BACKGROUND: Detection of Salmonella in patients with enteric fever by culturing of blood is considered the gold standard method as a result of its high specificity. However, it has low sensitivity and is time-consuming. Serological diagnosis by the widal testing has low sensitivity during the first week of infection and gives false positive results in endemic areas or where pre-infections are present. These drawbacks have encouraged the development of molecular detection methods for Salmonella Typhi detection. The PCR dependent diagnosis is considered a rapid and sensitive technique.

OBJECTIVES: Rapid detection of Salmonella spp. directly from blood by PCR, culture and serology with comparison of PCR, culture and serology for diagnosis of typhoid fever.

STUDY DESIGN: Comparative cross sectional study.

PARTICIPANTS: 100 cases of suspected Typhoid fever.

METHODS: Venous blood samples were collected from patients under all aseptic precautions & divided into 3 parts- 5 ml used for Culture, 2ml for Widal and 1 ml for PCR analysis. For culture, FA bottles of BacT/ALERT^® Blood Culture Bottles (BioMerieux, Inc. Durham, NC 27712) were used and identified by VITEK2 Compact system.

RESULTS: Widal testing was done using a cut-off of ≥ 1: 160, 58.89% patients showed positive titers and 41.11% had negative titers. Culture was positive in 57.0% patients, out of which 82.2% showed growth of Salmonella Typhi, 13.3% showed growth of Salmonella Paratyphi A and 4.4% showed growth of Salmonella Paratyphi B. PCR was positive for 87.0% patients and negative for 13% for Salmonella spp. Sensitivity and specificity of PCR was 91.1% and 61.8% respectively when compared to culture. Sensitivity and Specificity of widal with respect to PCR was of 66.6% and 58.3% respectively. With PCR as gold standard, culture showed a sensitivity of 75.9% and specificity of 84.0%.

CONCLUSIONS: PCR is a fast, accurate and reliable technique for diagnosis of typhoid fever.

 IMPLICATIONS: The PCR technique is fast and effective diagnostic test at any stage of the disease even when the antibiotics have been started or in the situations where pathogen load is very low.