Page 25 - Epidemiological studies on tuberculosis control and respiratory viruses

Distribution of respiratory viruses by illness severity in adults
Introduction
Rapid and accurate detection of viral pathogens facilitates early diagnosis, early identification of outbreaks, timely intervention, effective management of high-risk contacts, appropriate antimicrobial therapy, and avoidance of unnecessary laboratory testing [1]. The introduction of real-time polymerase chain reaction (RT-PCR)-based methods has greatly improved the diagnostics for respiratory viral infections. However, detection of a viral pathogen by RT-PCR does not necessarily imply causality of the illness; it is well established that subclinical respiratory viral infections do occur. Moreover, because of its high analytic sensitivity, RT-PCR may detect small amounts of viral nucleic acids, the clinical relevance of which may be difficult to interpret since, for example, these may reflect past or asymptomatic infections [2]. Multiple studies have demonstrated a correlation between viral load of respiratory viruses and severe disease [3] [4] [5] [6] [7]. Hence, quantitation of viral nucleic acids may be helpful for the clinical interpretation of a positive PCR result.
Understanding the clinical significance of respiratory viral infections is essential
for improving preventive and therapeutic strategies. Most etiological studies have
focused on patients presenting in health care settings with respiratory illness.
However, studies in the general population could provide information on the
background prevalence of respiratory viral infections and thereby contribute to our
understanding of the clinical interpretation of a positive PCR result in patients with
respiratory illness who are seeking health care. Therefore, the objective of our study
was to compare the prevalence and relative distribution of respiratory viral infections 6 among adult populations that vary in illness severity, ranging from asymptomatic
or mildly symptomatic individuals in the general population not seeking healthcare to patients with severe disease requiring intensive care, and to evaluate whether viral load estimations could aid in the interpretation of diagnostic test results. A population-based cohort study provided the opportunity to study the prevalence, relative distribution and viral load of respiratory viral infections in the adult general population. For comparison, demographic data and routine diagnostic test results were used from adult patients who, during the same period as the cohort study, were presented or admitted to a large tertiary referral hospital which also provides non- tertiary care for the catchment area of the cohort study population.
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