Association Between Real-time Polymerase Chain Reaction Cycle Threshold Value and Clinical Severity in Neonates and Infants Infected With Bordetella pertussis.

ABSTRACT

BACKGROUND: Polymerase chain reaction (PCR) is highly sensitive and is thus the standard method for diagnosing pertussis. Real-time PCR is widely used because of its accuracy and the simplicity of the simultaneous cycle threshold (Ct) value, which represents the copy numbers of the target gene. Little is known of the association of Ct value with pertussis severity in neonates and infants. METHODS: This study determined Ct values in neonates and infants diagnosed with pertussis by real-time PCR using nasopharyngeal samples at Vietnam National Children's Hospital in Hanoi in 2017 and 2019. The association of disease severity and clinical parameters were analyzed using univariate and multivariate analyses. RESULTS: We evaluated 108 patients with pertussis [median age 63 days, interquartile range (IQR) 41-92 days]. Only 6/108 (6%) received at least 1 dose of a pertussis-containing vaccine. Among them, 24 (22.2%) had severe disease requiring care in a pediatric intensive care unit, 16 (13.8%) required mechanical ventilation, and 3 (2.6%) died. The median Ct value was lower in patients with severe disease (19.0, IQR 16.5-22.0, n = 24) than in those without severe disease (25.5, IQR 20.0-30.0, n = 84) (P = 0.002). Logistic regression analyses demonstrated that PCR Ct value [odds ratio (OR) 1.783, 95% confidence interval (CI) 1.013-3.138, P = 0.045], age (OR 3.118, 95% CI 1.643-5.920, P = 0.001), and white blood cell counts (OR 0.446, 95% CI 0.261-0.763, P = 0.003) remained significantly associated with severe disease. CONCLUSIONS: Real-time PCR Ct values for pertussis might be useful as a predictor of severe disease in neonates and infants.