The time trend of respiratory pathogens was analyzed by dividing the study period into 2 weeks. A total of 11 types of pathogens are separated into 4 groups, which are non-SARS-coronaviruses, FluA and FluB, atypical bacteria (M. pneumoniae and Chlamydia) and other viruses. The frequency of FluA/B and non-SARS-coronaviruses decreased and reached 0% thereafter. At weeks 3–4, the peak frequency observed in the other viruses’ group was 89%, followed by a progressive decline (Fig. 1E). The total number of samples tested also showed this decreasing pattern. In contrast, within the same time interval, the positive detection rate of atypical bacteria increased rapidly, 20% at weeks 3–4, peak at weeks 9–10 as 44%, and at weeks 15–16 fell to 9%. This patten is completely different from previous years.
Comparing the 2016–2019 data with the distribution in the same period of 2020, we found that the FluA/B group showed a rapid upward trend in the first 4 weeks of 2017–2019, and then gradually declined (Fig. 1). In 2016, the frequency rose to 60% within weeks 1–8, and then fell back to 4% at week 9, of which FluB accounted for a large proportion (Fig. 2). However, the pattern of 2016–2019 is quite different from that of 2020, which maintained a downward trend without any peak.
Non-SARS-coronaviruses were distributed steadily during the 2016–2019 observation period. In addition to rising to 10% in weeks 11–16 of 2017, the positive rates in 2016, 2018 and 2019 remained below 5%. While in 2020, especially after week 9, there are basically no positive specimens.
The positive detection rates of M. pneumoniae and Chlamydia in the observation period of 2016–2019 were steadily distributed between 5%-15%. However, in 2020, when the positive rates of all other viruses began to decrease, the positive rates of M. pneumoniae and Chlamydia increases and reaching a peak of 44% in 10th week.
The positive rates of other pathogens remained at around 80% in the first 16 weeks of 2016–2019, while in 2020, it fell from 89% to less than 20%.
By comparing each pathogen separately, we found that the following pathogens distribution trends in 2020 are significantly different from other years, including HRV, M. pneumoniae, HPIV, HMPV, FluA and HCoV, while the trends of RSV, FluB, AdV, Chlamydia, HBoV are similar among these five years (Fig. 2).