To study the presence and drug resistance of MP in throat swabs from ILI patients.

Throat swab specimens of 915 outpatients with ILI were collected from 17 grade A tertiary healthcare institutions in 15 regions of China (Weifang, Kaifeng, Harbin, Inner Mongolia, Beijing, Tianjin, Tongchuan, Xianyang, Qinhuangdao, Dandong, Hanzhong, Taiyuan, Benxi, Luohe, Nanyang) during two winters (one was from December 2018 to February 2019, and the other from December 2019 to February 2020) . The Influenza A+B Antigen Test Kit (Colloidal Gold) was used to identify influenza viral antigens. PCR was used to detect the nucleic acid from pneumonia pathogens. DNA sequencing was used to detect the drug-resistant gene associated with MP.

Of the specimens, 578 were from children (<18 years) and 337 from adults (≥18 years) . The overall detection rate of influenza viral antigens was 45.25% (414/915) . The positive rate of influenza A was 91.06% (377/414) . Pediatric and adult cases had no statistical difference in the detection rate of influenza viral antigens〔44.29% (256/578) vs 46.88% (158/337) , χ²=0.577, P=0.447〕. The overall detection rate of MP was 11.91% (109/915) . Pediatric and adult cases had no statistical difference in the detection rate of MP〔4.34% (25/578) vs 24.93% (84/337) , χ²= 86.094, P<0.001〕. Of the MP-positive specimens, 74.31% (81/109) had A2063G mutations, 1.83% (2/109) had A2064G mutations, and 1.83% (2/109) had A2063G and A2064G mutations. In children's MP-positive specimens, 48.00% (12/25) had A2063G mutations, 8.00% (2/25) had A2064G mutations, and 8.00% (2/25) had A2063G and A2064G mutations, the other 36.00% (9/25) had drug-susceptible strains. Of the adult MP-positive specimens, 82.14% (69/84) had A2063G mutation, 17.86% (15/84) had drug-susceptible strains, and no A2064G mutation was found. The rate of presence of drug-resistant gene A2063G mutations in adult specimens was higher than that in pediatric specimens (χ²=11.765, P=0.001) . Both influenza viruses and MP were detected in 2.84% (26/915) of the specimens. The rate of co-presence of influenza viruses and MP in adult specimens was higher than that in pediatric specimens〔4.75% (16/337) vs 1.73% (10/578) , χ²=7.022, P=0.008〕.

During winters in 2018—2020, influenza A was the major type of influenza prevailing in northern China. MP infection was not rare in patients with ILI, and it was more common in adults than in children. The resistance rate of MP to macrolide antibiotics was relatively high. A2063G mutation in the 23SrRNA gene was the major type of mutations. Some cases were coinfected with influenza viruses and MP.