Background and aim: Mycoplasma pneumoniae (Mp) is a common cause of lower respiratory tract infections (LRTI) in children. Nevertheless, it can also cause several extrapulmonary manifestations. Factors determining clinical outcome and clinical severity of Mp infections are only partly understood. Mp strains can be classified into two genetic groups called P1 type 1 (P1-1) and P1 type 2 (P1-2) based on the DNA sequence of the P1 adhesion protein gene. Multiple-Locus Variable number tandem repeat Analysis (MLVA) offers a more discriminative categorization of strains. It is mainly unknown if Mp genotype is associated with the clinical outcome of Mp infections in children. By investigating clinical features of patients with an acute Mp infection, we aimed to determine if Mp genotype is associated with the presentation and severity of acute infection in children.
Methods: We performed a retrospective study of children referred to University Children’s Hospital Ljubljana and Department of Infectious Diseases Ljubljana with signs of acute Mp infection from January 2014 to December 2014. All patients 䁤18 years who were PCR-positive for Mp from pharyngeal swabs were recruited for the study. We excluded patients who did not show signs of acute infection and cases where additional testing provided evidence that other infectious or non-infectious agents were the more likely cause of the disease. The patients were further divided into groups according to clinical outcome and Mp P1 and MLVA genotype. Firstly, we assessed the association between Mp P1 and MLVA genotype and a specific clinical outcome. Secondly, we compared epidemiological and clinical data of patients with LRTI, infected with either P1-1 or P1-2, and between the most frequent MLVA strains. Thirdly, we compared epidemiological and clinical data of patients with cutaneous disease, infected with either P1-1 or P1-2, and between the most frequent MLVA strains. Lastly, the characteristics of patients with PCR-positive Mp infection were compared to those of patients who tested PCR-negative for Mp.
Results: In the study period, 1621 children were referred to our hospitals with signs of acute Mp infection. After applying the inclusion and exclusion study criteria, we evaluated data from 482 patients (260 (54 %) boys and 222 girls (46 %), mean age 6,9 years; standard deviation (SD) 3,4 years). The most frequent clinical outcome in our patients were LRTI, observed in 88 % of cases (425/482). Thirteen percent of children (62/482) presented with an extrapulmonary clinical outcome. Of those, cutaneous disease was the most frequent, observed in 9 % of cases (45/482). We found no association between Mp genotype and a specific pulmonary and extrapulmonary clinical outcome in our sample of patients with acute Mp infection. Data from 310 patients with LRTI infected with P1-1 were compared with 110 patients infected with P1-2. P1-2-infected children over five years presented with significantly higher inflammatory marker levels and were admitted to the hospital more often. In addition, we compared the data of patients with LRTI infected with the three most common MLVA types: MLVA-3,5,6,2, MLVA-3,6,6,2, and MLVA-4,5,7,2. MLVA-3,5,6,2-infected patients older than five years presented with significantly higher inflammatory marker levels than MLVA-3,6,6,2- and MLVA-4,5,7,2-infected patients. Infections with MLVA-3,6,6,2 strains were more frequent in admitted patients with cutaneous disease compared to other MLVA strains. Age, duration of symptoms, and chest radiographic findings had the highest predictive value for Mp LRTI in a multivariable logistic regression model.
Conclusions: In our research we found no association between Mp P1 and MLVA genotype and a specific pulmonary and extrapulmonary clinical outcome. However, the results from our large cohort indicate that Mp genotypes may have different pathogenic potentials, which was especially observed when comparing markers of disease severity of patients with LRTI and cutaneous disease older than five years.
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