MAB8581 Sigma-AldrichAnti-RSV Antibody, fusion protein, all type A strains, clone 92-11C

BACKGROUND: Human respiratory syncytial virus (hRSV) detection in nasopharyngeal aspirates (NPAs) from infants with acute respiratory tract infection (ARTI) does not prove the hRSV etiology of the current ARTI episode. HRSV RNA quantification may help in affording this issue. OBJECTIVES: hRSV was detected by quantitative reverse transcription-PCR in NPAs taken upon admission to hospital and, whenever possible, at discharge and subsequent medical visits. STUDY DESIGN: Prospective study, including 63 infants affected by either hRSV upper or lower ARTI. RESULTS: Based on the kinetics of viral load, hRSV etiology was identified in 25 infants in whom hRSV load dropped from 2.5 x 10(6) upon admission (presence of respiratory symptoms) to 7.5 x 10(2)RNAcopies/ml NPA upon discharge (absence of symptoms) after a median time of 5 days, and in 19 infants, in whom hRSV load was determined at admission only, in association with clinical symptoms (2.4 x 10(6)copies/ml). Furthermore, low levels of hRSV RNA (1 x 10(5)copies/ml NPA) identified 14 patients with non-hRSV ARTI. Finally, in 14 infants with hRSV coinfections or sequential infections, hRSV quantification defined the hRSV role in the current ARTI episode. CONCLUSIONS: hRSV RNA quantification is critical in defining the hRSV role in respiratory infections.

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory infection of children. Understanding RSV pathogenesis and evaluating interventions requires quantitative RSV testing. Previous studies have used the plaque assay technique. Real-time reverse transcriptase PCR (RTrtPCR) offers possible greater sensitivity, stability after freeze/thaw, and lower cost, thus facilitating multicenter studies. We developed RTrtPCR assays based upon the RSV N and F genes. The N-gene assay detected greater RSV quantity and was further evaluated. Standard curves utilized both extractions from RSV culture supernatants of known quantity and cloned purified copies of the target DNA. In vitro, the ratio of RSV subgroup A (RSV-A) genome copies to PFU was 153:1. A total of 462 samples collected quantitatively from 259 children were analyzed in duplicate by RTrtPCR. Results were compared with those of RSV plaque assays performed on fresh aliquots from the same children. Duplicate RTrtPCR results were highly correlated (r2 = 0.9964). The mean viral load from nasal washes obtained on the first study day was 5.75 +/- standard error of the mean 0.09 log PFU equivalents (PFUe)/ml. Viral load by RTrtPCR correlated with plaque assay results (r2 = 0.158; P less than 0.0001). Within individuals, upper and lower respiratory tract secretions contained similar viral concentrations. RSV-A-infected children had 1.17 log PFUe higher viral loads than did those with RSV-B (P less than 0.0001). RSV quantification by RTrtPCR of the N gene is precise and has significant, though limited, correlation with quantitative culture. The utility of the RTrtPCR quantification technique for clinical studies would be solidified after its correlation with RSV disease severity is established.

Heterogeneity in respiratory syncytial virus (RSV) disease severity likely is due to a combination of host and viral factors. Infection with RSV subgroup A is thought to produce more severe disease than RSV-B. Higher RSV loads correlate with greater disease severity in hospitalized infants. Whether subgroup-specific variations in disease severity result from differences in RSV load has not been studied. A total of 102 RSV-hospitalized infants less than 2 y of age were studied. Nasal washes were collected in a standardized manner and were cultured in less than 3 h in parallel with an RSV quantitative standard in a HEp-2 plaque assay. RSV-A (72%) was more frequent than RSV-B. Disease severity risk factors were similar between subgroups. RSV loads were similar between A and B subgroups (4.77 versus 4.68 log PFU/mL). Measures of disease severity were also similar between subgroups.