Association of the C sub(T) values of real-time PCR of viral upper respiratory tract infection with clinical severity, Kenya

• Published in: Journal of medical virology Vol. 85; no. 5; pp. 924 - 932
• Main Authors: Fuller, James A, Njenga, MKariuki, Bigogo, Godfrey, Aura, Barrack, Ope, Maurice O, Nderitu, Leonard, Wakhule, Lilian, Erdman, Dean D, Breiman, Robert F, Feikin, Daniel R
• Format: Journal Article
• Language: English
• Published: 01.05.2013
• Subjects: Adenovirus; Human metapneumovirus; Influenza virus; Parainfluenza virus; Respiratory syncytial virus
• ISSN: 0146-6615; 1096-9071
• DOI: 10.1002/jmv.23455

Quantitative real-time polymerase chain reaction (qRT-PCR) assay of the upper respiratory tract is used increasingly to diagnose lower respiratory tract infections. The cycle threshold (C sub(T)) values of qRT-PCR are continuous, semi-quantitative measurements of viral load, although interpretation of diagnostic qRT-PCR results are often categorized as positive, indeterminate, or negative, obscuring potentially useful clinical interpretation of C sub(T) values. From 2008 to 2010, naso/oropharyngeal swabs were collected from outpatients with influenza-like illness, inpatients with severe respiratory illness, and asymptomatic controls in rural Kenya. C sub(T) values of positive specimens (i.e., C sub(T) values<40.0) were compared by clinical severity category for five viruses using Mann-Whitney U-test and logistic regression. Among children <5 years old we tested with respiratory syncytial virus (RSV), inpatients had lower median C sub(T) values (27.2) than controls (35.8, P=0.008) and outpatients (34.7, P<0.001). Among children and older patients infected with influenza virus, outpatients had the lowest median C sub(T) values (29.8 and 24.1, respectively) compared with controls (P=0.193 for children, P<0.001 for older participants) and inpatients (P=0.009 for children, P<0.001 for older participants). All differences remained significant in logistic regression when controlling for age, days since onset, and coinfection. C sub(T) values were similar for adenovirus, human metapneumovirus, and parainfluenza virus in all severity groups. In conclusion, the C sub(T) values from the qRT-PCR of upper respiratory tract specimens were associated with clinical severity for some respiratory viruses. J. Med. Virol. 85:924-932, 2013. [copy 2013 Wiley Periodicals, Inc.