PCR associated with limited diagnostic utility in viral URI

Image: CDC/ Hsi Liu, Ph.D., MBA, James Gathany

1. Through use of quantitative PCR (qPCR) to evaluate viral infection in a cohort of pediatric patients with and without respiratory symptoms, researchers found that symptomatic patients were more likely to be infected with human bocavirus, parainfluenza, and metapneumovirus than asymptomatic patients. qPCR detection of common viruses such as rhinovirus and adenovirus was no more likely in symptomatic or asymptomatic patients.

2. Coinfection with more than 1 viral strain was more common in patients with respiratory symptoms than in control patients, and patients with symptoms and viral coinfection were more likely to have increased respiratory rate, tachycardia, and decreased oxygen saturation.

Evidence Rating Level: 3 (Average)

Study Rundown: Quantitative real-time polymerase chain reaction (qRT PCR) is a laboratory test that amplifies and identifies viral DNA or RNA. The use of PCR for diagnosis of viral infection has been introduced as a sensitive diagnostic tool in the clinic setting. This matched case-control study evaluated PCR as a diagnostic tool for acute respiratory infections (ARI). qRT PCR was used to identify viral isolates in nasopharyngeal samples from patients with and without upper respiratory infection symptoms. Researchers found that parainfluenza virus, human bocavirus, and metapneumovirus were more frequently found in patients with respiratory symptoms, while detection of corona virus, rhinovirus, and adenovirus were common among both case and control populations. Coinfection was more common among patients with symptoms than those without (20.1% and 5.3%, respectively), and patients with respiratory symptoms and coinfection were found to have more severe disease than those with a single infection. This study was limited by lack of follow-up of control studies after sampling, so early diagnosis of later infection is possible. Furthermore, the qRT PCR method employed in this study was not designed to evaluate viral load, a factor related to disease severity. This study suggested that qRT PCR may have limited utility in clinical diagnosis of respiratory infections because of the high prevalence of common viral strains in both symptomatic and asymptomatic individuals and because of the increased likelihood of viral coinfection in symptomatic patients.

Click to read the study in Pediatrics

Relevant Reading: Infections of the lower respiratory tract: old viruses, new viruses, and the role of diagnosis

In-Depth [matched case-control study]: This study included a cohort of 229 children (mean age = 10 months, 59.3% male) less than 5 years old who presented to a Swedish pediatric emergency department with ARI symptoms (coryza, rhinorrhea, sore throat, cough, ear ache, or dyspnea) and matched them to a cohort of control patients without ARI symptoms. Nasopharyngeal aspirates were tested via qRT PCR for common viral strains. One hundred and fifty one (72.3%) case patients and 74 (35.4%) control patients had detectible viral infection. Human bocavirus, metapneumovirus, and parainfluenza were detected more frequently in case patients. Odds ratios (ORs) for infection in the case group for these viruses (adjusted for variables associated with ARI in initial univariate analyses) were 4.4 (95% CI: 1.6-11.8), 12.0 (95% CI: 2.0-71.6), and 33.6 (95% CI 3.8-294.4), respectively.  Forty-two (20.1%) patients with respiratory infection symptoms tested positive for more than 1 viral strain, with an unadjusted OR for coinfection of 12.3 (95% CI: 5.0 to 30.4). Patients with symptoms and viral coinfection were more likely to have increased respiratory rate (P = 0.009), tachycardia (P = 0.05), decreased oxygen saturation (P = 0.04), discharge diagnosis of pneumonia (P = 0.006), and bronchitis (P = 0.02). Patients later identified as having croup, bronchitis or asthma, were also most likely to test positive for more than 1 virus (88%).

More from this author: AAP urges bottle feeding over breastfeeding in mothers with HIV, Pediatric influenza burden remains high despite new vaccination recommendations, Cow’s milk consumption linked to increased vitamin D and decreased iron stores in early childhood

©2012-2014 2minutemedicine.com. All rights reserved. No works may be reproduced without expressed written consent from 2minutemedicine.com. Disclaimer: We present factual information directly from peer reviewed medical journals. No post should be construed as medical advice and is not intended as such by the authors, editors, staff or by 2minutemedicine.com. PLEASE SEE A HEALTHCARE PROVIDER IN YOUR AREA IF YOU SEEK MEDICAL ADVICE OF ANY SORT.