RESUMO
Objective:To clarify the clinical characteristics and related fators of children with delayed antibody production of mycoplasma pneumoniae pneumonia(MPP).Methods:Two hundreds and eithty-five cases of children hospitalized at Children′s Hospital of Soochow University with MPP(positive for nucleic acid testing of respiratory secretion)were chosen from January 1st, 2019 to September 31st, 2019.Delayed antibody production group included 36 cases, who were tested for negative IgM antibody meanwhile the titer of IgG antibody changed less than 4 folds within 14 days.Positive group included 249 cases who were tested for positive IgM antibody or the titer of IgG antibody changed over 4 folds within 14 days.The characteristics of clinical manifestation, immunology and radiology were comparatively analyzed.Results:The medium age of delayed antibody production group was 0.75(0.30, 2.78)years old, which was obviously younger than that from positive group[5.50(3.73, 7.20)years old]( P<0.001). Low level of serum immunoglobulin IgG was the independent effect factor of delayed production for Mycoplasma pneumoniae antibody( P=0.037). When the serum immunoglobulin IgG level was lower than 7.155mmol/L, the sensitivity of predicting delayed production for mycoplasma pneumoniae antibody would be 0.819 and the specificity was 0.833.The underlying diseases associated with delayed antibody production were hospitalization history during neonatal period( P=0.007)and congenital heart disease( P=0.001). There were 11.11%(4/36)of children appearing spasmodic cough, 41.67%(15/36)of children showing wheezing and 33.33%(12/36)showing diarrhea in delayed antibody group, which were significantly higher than those in positive group[0.40%(1/249), 24.50%(61/249)and 9.64%(24/249), respectively, P<0.05]. The incidence of fever in delayed antibody group were 63.89%(23/36), which was lower than that in positive group[92.37%(230/249)]( P<0.001), meanwhile, the fever last time was 2.50(0, 4.75)days in delayed antibody group, which was shorter than that in positive group[ 7(5.00, 8.50)days]( P<0.001). In the delayed antibody group, there was 19.44%(7/36)of children sufferring from lobar pneumonia, and no extrapulmonary manifestations occurred, which were significantly lower than those in positive group[75.50%(188/249), 14.86%(37/249)]( P<0.05). Conclusion:Delayed antibody production in children with MPP is more common when serum immunoglobulin IgG level is lower than 7.155 mmol/L, especially in the presence of neonatal hospital history and congenital heart disease.The clinical manifestations of these children are mainly characterized by spasmodic cough and wheezing, with low probability of fever, lobular pneumonia and extrapulmonary manifestations.