Page 48 - Epidemiological studies on tuberculosis control and respiratory viruses
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Chapter 7
load might have prognostic value given its relation with illness severity. In addition, viral load measurements may be important to monitor the effect of antiviral therapy and detect treatment failure, e.g. due to development of drug resistance, early in course of treatment.
Few other studies investigated associations between quantitative PCR results of viral pathogens and illness severity in a study population consisting of both asymptomatic and symptomatic individuals. These studies show conflicting results. For instance, Jansen and colleagues also found higher InfA viral loads in symptomatic patients than in asymptomatic controls, but, in contrast to our findings, they also found significant higher RV and hCoV viral loads among symptomatic individuals (40). Fuller and colleagues did not find any association between InfA loads and illness severity (43). These contradicting results might be due to the lack of validated definitions of illness severity, usage of different PCR assays, or could be the result of heterogeneous study populations, e.g. our study population consisted of adults while most etiological studies, including the study by Jansen and colleagues, focus on children (40) (44).
Further research
Prospective studies with larger sample sizes and inclusion of different spectra of respiratory disease and infectious etiologies are clearly needed before viral load can be used as an additional interpretive parameter in clinical practice. Given the obvious need for improved diagnostics, it might be more rewarding to search for other parameters of pathogenicity to assist patient classification. Detailed analysis of the host response to infection by different pathogens could be such an alternative approach (45). Each infectious agent interacts with specific pattern-recognition receptors differentially expressed on human blood leukocytes, which thus constitute an accessible source of clinically relevant information (46). In fact, recent transcriptional profiling studies have demonstrated pathogen-specific gene-expression profiles detected in the peripheral blood of patients with acute infections (45) (47) (48). Gene-expression profiling can increase our knowledge on the pathogenesis of infections and biomarkers of disease severity, and thus might be a suitable candidate to assist in treatment decisions (46).
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