Variation in serum antibody titers in children with community-acquired mycoplasma pneumoniae pneumonia

Mycoplasma pneumoniae pneumonia (MPP) is one of the most common primary atypical pneumonias caused by mycoplasma pneumoniae (MP). Its early diagnosis is difficult. In this study, we examined the variation in serum antibody titers in children with MP infection and explored its early diagnostic value. This prospective case series involved 134 children with MP infection. Serum antibody detection was performed with a commercially available particle agglutination test (SerodiaMyco II; Fujirebio, Tokyo, Japan). The chi-squared test was used to identify significant associations between disease duration and the rate of serum antibody positivity. Linear correlation and simple linear regression were used to describe the relationship between the mixed antibody titer and disease duration. Positivity rates (serum antibody titer >= 1:160) at 4-7 days, 8-14 days, and 15-21 days were 41.7%, 91.6%, and 100%, respectively, with significant differences among timepoints. Log (IgA + IgM + IgG)(-1) was correlated positively with disease duration (r = 0.832, P < 0.01). Of 85 children with community-acquired MPP showing a fourfold or greater increase in serum antibody titer at a 2-week interval, 75 (88.24%) children showed such an increase at a 1-week interval. The present study demonstrated that the serum antibody titer is related closely to the duration of MP infection, and suggest that a 2-week interval is not needed for the diagnosis of MP infection using paired serum tests. This finding may have great diagnostic value, enabling short-term retesting for the diagnosis of MP infection.