Netherlands sees unexpected surge in Mycoplasma pneumoniae cases, younger population more affected

In a recent study published in the journal Eurosurveillance, a team of researchers from the Netherlands reported on the recent increase in Mycoplasma pneumoniae infections in the country and compared it to past trends across the country and Europe.

Study: Increased incidence of Mycoplasma pneumoniae infections and hospital admissions in the Netherlands, November to December 2023. Image Credit: Kateryna Kon / Shutterstock

Background

Mycoplasma pneumoniae is among the most common etiological agents of upper and lower respiratory tract infections across all ages. The bacterium causes recurrent epidemics across the globe, with the last epidemic in Europe occurring between 2019 and 2020. Infections with M. pneumoniae also result in encephalitis and lesions in the mucous membrane known as erythema exsudativum multiforme.

The incidence of M. pneumoniae infections in the Netherlands has been low for several years. However, a regional hospital has recently seen a sudden increase in cases involving M. pneumoniae infections, causing researchers to wonder whether a similar trend in incidence has been observed nationwide and across Europe.

About the study

In the present study, the researchers used data obtained from the Regional Public Health Laboratory Kennemerland, which is the diagnostic center for the Spaarne Gasthuis Regional Hospital, to gain insights into the recent increase in M. pneumoniae infections at the hospital. The data included the number of detected cases of M. pneumoniae infections and hospital admissions from 2017 to 2023, as well as demographic information of all the patients, such as age, sex, intensive care unit admissions, and hospital admission duration.

Hospital admissions were attributed to M. pneumoniae infections if they were preceded by the detection of M. pneumoniae through a polymerase chain reaction (PCR) test using an oropharyngeal or nasopharyngeal swab at most two days before the admission.

Additionally, to determine the national trends in M. pneumoniae infections, information from across the Netherlands was obtained from a surveillance system operated by the Dutch National Institute for Public Health and the Environment, which receives data on the type and number of pathogens being detected by the Dutch Working Group on Clinical Virology belonging to the Dutch Society for Clinical Microbiology. This data does not include information on the methods used for detecting the pathogen or demographic information about the patients.

Furthermore, the researchers also used data from a digital surveillance system where information on respiratory symptoms has been collected from 2020 onwards from voluntary participants above 16 years of age belonging to the resident population of the Netherlands.

The National Public Health Institute in the Netherlands had also instructed subsets of individuals experiencing respiratory symptoms to provide oropharyngeal or nasopharyngeal swabs, which were analyzed weekly. The data from these PCR tests were also included in the assessment of the national trends in M. pneumoniae infections.

Results

The findings suggested that the regional hospital of Spaarne Gasthuis and the Netherlands overall experienced a significant increase in the number of cases of M. pneumoniae infections since October 2023. The number of hospital admissions associated with M. pneumoniae infections at the regional hospital had also increased during this period. Furthermore, the median age of the patients was significantly lower (28 years) as compared to the epidemic that occurred between 2019 and 2020, where the median age was 40.

The study found that out of the 133 patients who were admitted to the regional hospital due to M. pneumoniae infections, 55 were below 18 years of age, with 27 patients between the ages of five and 11 years. Even among adults, most patients were of the younger age groups of 18 to 29 years and 30 to 39 years. In comparison, the previous epidemic from 2019 to 2020 saw a total of 68 cases of M. pneumoniae infections, with a significantly higher median age of the patients. The researchers also observed similar trends in Denmark.

While the reason for this sudden increase in M. pneumoniae infections is not yet known, the researchers speculated that it could be either due to a shift in the dominant M. pneumoniae strain or as a consequence of a decrease in social interactions and other non-pharmaceutical interventions implemented during the coronavirus disease 2019 (COVID-19) pandemic. They believe that these interactions could have lowered the herd immunity against M. pneumoniae.

Conclusions

Overall, the findings indicated that the Netherlands had experienced a sudden increase in the incidence of M. pneumoniae infections since October 2023. Furthermore, compared to the previous epidemic, the median age of the patients was significantly lower at 28 years, indicating that younger individuals seemed to be more susceptible to this strain. The researchers believe that more data on disease severity and the circulating M. pneumoniae strains is required to understand this current trend of M. pneumoniae infections.