Virological Diagnosis of Influenza Viruses in Zagazig University Hospitals

Abstract

Influenza-like illness is a nonspecific respiratory illness characterized by fever, fatigue, cough, sore throat, headache and other symptoms that stop within a few days. Aim of the work: Aim of this study was to expect influenza virus as a cause of influenza like illness depending on signs and symptoms and to compare rapid techniques and viral isolation for its diagnosis. Determine whether nasal or throat swabs are superior specimens to detect the seasonal influenza virus by measuring viral load in all specimens by real time RT-PCR. Compare qPCR assays with conventional RT-PCR to assess its potential application in routine surveillance and diagnosis. Subjects, materials & methods: This study carried out in Medical Microbiology and Immunology department, Faculty of Medicine, Zagazig University. The study included 75 patients, 46 were males and 29 were females with ages ranging from 4 days to 65 years old (median=19). Nasopharyngeal swabs were obtained from all patients after 2 or 3 days of onset and were subjected to fluorescence detection of the viruses directly in the samples and a trial to isolate the viruses by cell culture on MDCK cells. One nasal and one throat swab were obtained from every patient and examined for influenza virus detection by both conventional and real time RT-PCR. Results: Indirect fluorescence test performed directly on the nasopharyngeal samples revealed 23 positive cases out of 75. The cell culture revealed that 22 out of 75 cases were confirmed as influenza. In comparing Fluorescence versus the cell culture as the gold standard, its sensitivity =90.9%, specificity =94.3% and accuracy =93.3%. Positive predictive value =86.9% and Negative predictive value =96.1%. As regard Fluorescence before and after cell culture technique, it was statistically non significant. Age group (<2 years) was the most susceptible age group to influenza disease and there was male predominance (61.3%). Real time PCR detected more positive samples when compared to conventional RT-PCR. There is direct correlation between throat and nasal swabs real time RT-PCR and this is statistically significant. The mean, median, standard deviation and range of viral load by nasal swabs are higher than those of throat swabs denoting that nasal swabs are more useful diagnostic tools in diagnosis of influenza than throat swabs.