Why is it particularly serious this year? , Mycoplasma pneumonia has peaked in many places around the world

This winter, respiratory diseases have entered a period of high incidence. Since October, the number of children with respiratory diseases in pediatric hospitals in many places across the country has increased significantly, especially the increase in children with Mycoplasma pneumoniae infection, which has caused concern.

Recently, mycoplasma pneumonia has caused a wave in many places around the world. What exactly is mycoplasma pneumonia? Will it cause a new round of global epidemic? Why do you feel that mycoplasma pneumonia infection is particularly severe this year?

First of all, it should be pointed out that mycoplasma pneumonia is a common respiratory disease, and children and adolescents are more susceptible to infection. However, Mycoplasma pneumoniae is not a new pathogen and will not cause a new round of large-scale epidemics.

In China, mycoplasma pneumonia infections have shown a trend of rising first and then falling.

According to media reports, since September and October, mycoplasma pneumonia infections have increased significantly in many hospitals in many provinces and cities in China.

For example, the number of children infected with Mycoplasma pneumoniae has increased significantly since September in many hospitals in Beijing, Chongqing, Shanghai, Henan, and Hebei, and the number of outpatients and inpatients has increased significantly. According to data previously disclosed to the media from the outpatient and emergency departments of Shanghai Children's Medical Center, starting in October, the positive detection rate of Mycoplasma pneumoniae RNA in the hospital increased from 20% to 30% to about 50%.

However, the above data conclusions are basically based on the hospital level, and the data trends of different hospitals in different regions are different. For example, Shanghai Children's Medical Center treats nearly 400 children with mycoplasma pneumonia, which has doubled compared with previous years. Liu Maosong, an attending pediatrician at the Baoshan Branch of Renji Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, said that mycoplasma pneumoniae infections occur throughout the year. Everyone is infected, especially when the body's immunity is reduced. Although the number of outpatient and emergency visits has increased significantly in recent months, it is only about half of what it was before 2019.

Since the overall surveillance data has not been made public, it is still difficult to determine whether mycoplasma pneumonia infections are higher than in previous years.

On November 23, the Chinese Centers for Disease Control and Prevention and the Chinese health department of Beijing Children's Hospital provided the WHO with relevant data on the increase in the incidence of respiratory diseases through a conference call, noting that since May, the number of outpatient and hospitalization cases in children caused by Mycoplasma pneumoniae has increased. increased. However, since October, there has been an increase in infections with a variety of known pathogens such as respiratory syncytial virus, adenovirus, and influenza virus, which has led to a recent increase in the number of outpatient and hospitalization visits among children, some of which occurred earlier than in history. No unusual or novel pathogens or unusual clinical manifestations have been identified.

The report also said China has established systems to obtain information on disease incidence trends and report these data to platforms such as the Global Influenza Surveillance and Response System.

According to the latest monitoring data, Mycoplasma pneumoniae infections have shown a decreasing trend in China since November.

Since mid-November, data from the outpatient and emergency departments of Shanghai Children's Medical Center show that the current positive detection rate of Mycoplasma pneumoniae RNA has dropped from 50% to 30%, and the number of influenza patients has been on the rise.

Wang Quanyi, deputy director of the Beijing Center for Disease Control and Chief Epidemiology Expert, also pointed out that according to the latest monitoring, the epidemic intensity of Mycoplasma pneumoniae has dropped to fourth among children's respiratory infectious diseases. From the perspective of the entire population, influenza, rhinovirus, and respiratory syncytial virus are the top three prevalent pathogens.

However, since the beginning of this year, the situation of mycoplasma pneumonia infections is indeed somewhat unusual. Not only in China, but also in many European countries such as Denmark, the Netherlands, and France, there has been a significant increase in infection cases.

Mycoplasma pneumonia infections in Denmark began to increase in the summer, but have risen sharply in the past five weeks, with 541 cases reported in mid-November, three times the number in mid-October.

In the Netherlands, more patients with pneumonia than in previous years visited their general practitioners since the beginning of August, but the number increased significantly from mid-September, and the number of children aged 5 to 14 years old with pneumonia increased to 130 per 100,000 children in late November, compared with Last year's peak was 1.2 times higher.

Data from France in early November shows that the number of children under 15 years old visiting emergency rooms and using SOS for outpatient treatment due to pneumonia has reached a record high in ten years. Mycoplasma pneumoniae pneumonia accounts for about 30% of all recent childhood pneumonia cases.

In addition, mycoplasma pneumonia infections are also higher than in previous years in Switzerland, Ireland and other places. In Warren County, Ohio, in the United States, there have been 142 pediatric cases since August. The number of cases is higher than the average and meets the definition of an epidemic by the state Department of Health. However, the U.S. Centers for Disease Control and Prevention said there are no abnormalities in cases nationwide.

Judging from the data trends published by various countries, mycoplasma pneumonia infections have basically increased since the summer, and it is not a sudden outbreak. A study published by The Lancet on November 23 monitored 24 countries around the world from April to September this year. Monthly data on mycoplasma pneumonia infections. Data show that since the beginning of this year, cases of mycoplasma pneumonia infections in Denmark, Sweden, Singapore, Switzerland and other places have increased rapidly since August.

Why will mycoplasma pneumonia show a global trend this winter?

An important reason is the immunity gap, that is, the difference between the level of herd immunity during the epidemic and before the epidemic.

Maria Van Kerkhove, acting director of the WHO Epidemic and Pandemic Preparedness Department, believes that the current epidemic of respiratory diseases in Chinese children is mainly due to the immunity gap, and the reason for this gap may be the non-pharmaceutical interventions implemented during the new crown epidemic, such as wearing masks, avoiding gatherings, Measures such as reducing travel.

Looking around the world, after the relaxation of epidemic prevention measures, most countries have faced the problem of an increase in respiratory diseases due to immunity gaps. Taking the United States as an example, the respiratory syncytial virus infection that raged in the United States in the autumn and winter of 2022 showed a non-seasonal trend after the COVID-19 pandemic subsided.

According to the Centers for Disease Control and Prevention, from 2017 to early 2020, RSV epidemics in the United States typically began in October and peaked in December or January. After the outbreak of the new coronavirus, due to the implementation of anti-epidemic measures such as isolation and wearing masks, there was no typical RSV epidemic in the 2020-21 epidemic season.

However, as the United States relaxes control, the 2021-22 epidemic season starts early in May, reaches its peak in July, and ends in January. The start and peak period of the 2022-23 epidemic season will be June and November respectively, later than the 2021-22 epidemic season but earlier than the pre-pandemic season. At the same time, the positive detection rate of PCR tests during this epidemic season is the highest in recent years, close to 20%.

In short, with the reduction of epidemic prevention and control, the risk of exposure of the group increases. Coupled with the gap in immunity level, the group is more susceptible to respiratory diseases including pneumonia.

In addition to the immune gap, Mycoplasma pneumoniae has attracted attention in many places around the world because of its "delayed onset" characteristics compared with other respiratory diseases.

In the later stages of the pandemic, as measures such as wearing masks, avoiding gatherings, and reducing travel eased, some respiratory diseases quickly resurfaced. The researchers noted that this pattern was most pronounced for seasonal viruses, such as influenza and respiratory syncytial virus. The RSV respiratory syncytial virus we mentioned above will have higher infection rates in the fall and winter of 2022 in the United States than before the epidemic.

According to data from a paper in The Lancet, as of September this year, the incidence rate of mycoplasma pneumonia has not reached the pre-COVID-19 epidemic figure. Before the epidemic, the global average incidence of mycoplasma pneumonia reached 8.61%. In 2020-2021 and 2021-2022, it dropped to 1.69% and 0.7% respectively. In 2022-2023, it was only 0.82%. The global average from April to September this year The incidence rate is approximately 4.12%.

This study points out that this may be because Mycoplasma pneumoniae takes more time to reproduce, has a longer incubation period, and has a relatively low transmission rate.

Since this "delayed appearance" may be unique to this Mycoplasma, studies in the field of epidemiology have suggested strengthening the atypical characteristics of distinguishing Mycoplasma pneumoniae from other pathogens, and doing a good job in monitoring Mycoplasma pneumoniae infection.

In general, Mycoplasma pneumoniae feels "menacing" this year, due to both the immune gap effect and the uniqueness of the pathogen itself.

In addition, after the epidemic, the increase in domestic testing methods and the increased awareness of patients and doctors about precise treatment have also caused "more detections" of Mycoplasma pneumoniae.

According to Dingxiangyuan, hospitals are increasingly using second-generation sequencing to detect mycoplasma infections. Compared with the traditional laboratory MP culture method, it is more accurate and improves the detection rate of clinical respiratory infection pathogens. Even if NGS is not used, doctors are now more inclined to test PCR on children for more accurate diagnosis and treatment.

But Mycoplasma pneumoniae infection itself is not as scary as everyone thinks, and it will not lead to a new round of pandemic.

In addition to Mycoplasma pneumoniae, various pathogens such as influenza virus, rhinovirus, and RSV have been active recently. Various places are still in a period of high incidence of respiratory infectious diseases. We should still pay more attention to protection, including washing hands frequently, opening windows frequently for ventilation, keeping warm, and taking appropriate doses. Protect your body and immune system through various means such as exercise to enhance immunity.