Influencing factors associated with cycle threshold values of nucleic acid amplification tests in nasopharyngeal swabs of children with pertussis

The median age was 3 months, the minimum age was 1 month, and the maximum age was 9 years and 8 months. Children aged 1-5 months accounted for 64.3%, children without pertussis vaccine accounted for 57.1%, children exposed to family respiratory tract infection accounted for 45.2%, children with spastic cough accounted for 71.4%, and the proportion of peripheral blood lymphocytes ≥ 60% accounted for 78.6%. The Ct values of the group aged 1-5 months was lower than that of the group aged over 6 months (28.9±4.0 VS 31.5±3.8, p<0.05).

The Ct values of the group without pertussis vaccination was lower than that of the vaccinated group (28.7±4.1 VS 31.2±3.7, p<0.05). The Ct values of the group exposed to family respiratory tract infection before onset was lower than that of the group without contact history (28.1±3.4 VS 31.2±4.1, p<0.05). The Ct values of the spastic cough group was lower than that of the non-spasmodic cough group (28.6±3.7 VS 32.8±3.4, p <0.01).

The Ct values of the peripheral blood lymphocyte ratio ≥ 60% group was lower than that of the peripheral blood lymphocyte ratio < 60% group (29.0±3.7 VS 32.7±4.2, p<0.05).Conclusion Children with pertussis less than 6 months old, not vaccinated with pertussis vaccine, contacting families with respiratory tract infection, having spastic cough and peripheral blood lymphocyte ratio ≥ 60% may have lower Ct values of nucleic acid amplification tests and may have higher infection load, which should be paid attention to by clinicians.