Should equivocal PCR results in children be reported to public health?

INTRODUCTION

Real-time polymerase chain reaction (PCR) is the preferred method for the diagnosis of pertussis. In Quebec, positive and equivocal results are reportable to public health; in contrast, in Ontario equivocal results are not reportable.

OBJECTIVE

To determine the clinical significance of equivocal, compared with positive results, in children with suspected pertussis.

METHODS

Retrospective cohort of consecutive patients seen at the Centre Hospitalier Universitaire Sainte-Justine in Montréal, Quebec, with suspected pertussis and tested with a bacterial multiplex PCR (including ) between 2015 and 2017. Medical records were reviewed using a standardized form. Univariate analyses (Student's t-test and chi-square test) and multivariable logistic regression were used to compare cases of positive and equivocal results.

RESULTS

Of the 1,526 multiplex PCR performed, 109 were positive and 24 equivocal. Both groups were similar in terms of demographics and disease severity assessments, but patients in the equivocal group had less paroxysmal cough (33.3% vs 79.8%, adjusted odds ratio [aOR] 0.11, 95% confidence interval [CI] 0.04-0.29) and whoop (0% vs 18.3%, <0.001), lower lymphocyte counts (6.6 vs 11.9 x10/L, =0.008), were more likely to be diagnosed with a viral co-infection (16.7% vs 3.7%, aOR 5.62, 95% CI 1.17-27.54) and were less likely to receive a macrolide (25% vs 89%, aOR 0.04, 95% CI 0.01-0.11). When admitted, patients with equivocal results had a shorter average length of stay (3.3 vs 12.2 days, =0.001).

CONCLUSION

Although there were similarities in disease severity, children with suspected pertussis who had equivocal PCR results had significantly different clinical presentations compared with those with positive results. In the context of limited public health resources, these results may inform the decision whether or not equivocal results need to be reported to public health by laboratories.