Emergence of Mycoplasma pneumoniae before and after COVID-19 pandemic in Germany

doi:10.21203/rs.3.rs-4907400/v1

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Emergence of Mycoplasma pneumoniae before and after COVID-19 pandemic in Germany

https://doi.org/10.21203/rs.3.rs-4907400/v1

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Purpose: Mycoplasma (M.) pneumoniae is a common pathogen of community-acquired pneumonia (CAP). Epidemics occur every 3-7 years especially in pediatric patients. We collected data from a large laboratory network in Germany to define the epidemiological dynamics in the pre- and post-COVID-19 pandemic period.

Methods: In this retrospective cohort study we included all patients that obtained targeted or multiplex PCR for M. pneumoniae from nasopharyngeal swabs, sputum or bronchoalveolar fluids from 2015 - 2024. Demographic data (age, sex, place of residence, in- or outpatient status) were compared between M. pneumoniae positive and negative patients and co-infections with bacterial or viral pathogens analyzed.

Results: We screened 38.204 patients for M. pneumoniae. 1448 cases (3.8 %) of M. pneumoniae were identified (48.8% females). Pediatric patients ≤18 years represented 75.7% of M. pneumoniae patients and 2.3% were ≥60 years. Incidence of M. pneumoniae increased in fourth quartile 2015 (16.2%), second quartile 2018 (14.8%) and fourth quartile 2023 (13.4%). No cases were detected during COVID-19 pandemic 2021. Young age, outpatient status and year of testing were predictors of M. pneumoniae detection in multivariate analysis (p<0.001).

Conclusions: Empirical treatment of CAP patients often does not include coverage of M. pneumoniae. A more thorough implementation of available surveillance data into clinical routine, respective therapies could be adapted more quickly during epidemic outbreaks of M. pneumoniae infections.

Mycoplasma pneumoniae

community-acquired pneumonia

epidemic

infection

Mycoplasma pneumoniae (M. pneumoniae) is one of the most common bacterial pathogens of community-acquired pneumonia (CAP). Estimates are that M. pneumoniae are accountable for 10–40% of CAP in children and 4–8% in adults during endemic periods [1, 2]. M. pneumoniae is most frequently detected during winter months. Incidences can rise to 40% in adults during epidemics which occur every 3–7 years [3]. M. pneumoniae can cause asymptomatic infection, mild, self-limiting disease or severe CAP [1, 4]. Co-infections with respiratory viruses are common in children [1]. Approximately 25% of patients have extrapulmonary manifestations including pericarditis, endocarditis, hepatitis, arthritis, encephalitis, aseptic meningitis, otitis and thrombosis [5]. Furthermore, M. pneumoniae is commonly linked to mucocutaneous disease including erythema multiforme, erythema nodosum, Stevens-Johnson syndrome and mucositis. Infections with M. pneumoniae increase the risk of childhood asthma and exacerbation of chronic lung disease and are a common cause of severe CAP in adults [4].

M. pneumoniae cannot be detected in routine microbiological diagnostics but special media for bacterial growth or testing by polymerase chain reaction (PCR) are needed. Therefore M. pneumoniae is presumably underdiagnosed. No reporting obligation exists for M. pneumoniae in Germany. During COVID-19 pandemic few cases of M. pneumoniae were reported from 2020–2022. Few data have been reported so far on rates of M. pneumoniae after the pandemic: Recent data show an increase of M. pneumoniae cases since 2023 in the USA and Europe [6–8]. We aimed to characterize M. pneumoniae detection before and after COVID-19 pandemic in Germany.

We conducted a retrospective cohort study including all patients with M. pneumoniae testing in respiratory samples from January 2015 – May 2024. Samples were sent to and collected at two large microbiology laboratories of the LADR Laboratory group Dr. Kramer & Colleagues that perform diagnostics for > 20.000 physicians and > 400 inpatient clinics especially from the North Western region of Germany. There were no exclusion criteria. Respiratory material included nasopharyngeal swabs, sputum and bronchoalveolar lavage fluids. Baseline characteristics of patients were date of sampling, age, sex, postal code and data on outpatient or inpatient sampling. Detected co-infection with other respiratory viruses and bacteria on multiplex PCR were analyzed. The study was approved by the ethics committee according to the declaration of Helsinki (number 2024-897167).

Microbiology

All analyses were performed at LADR. Three different PCRs were used to detect M. pneumoniae according to manufacturer’s specification (supplementary table 1): two multiplex PCRs (Allplex™ PneumoBacter Assay/Allplex™ RV Essential Assay by Seegene; Panel 1 and NxTAG® Respiratory Pathogen Panel Test by Luminex; Panel 2) including several bacterial and viral pathogens and a M. pneumoniae targeted PCR (ModularDx Kit M. pneumoniae, TibMolBiol). PCRs were performed according to the respective technical instructions in the different LADR laboratories upon request of the sending physician.

Statistics

Statistical analysis was performed using Jamovi (version 2.3.28.0) and R (version 4.2.2.). If more than one sample per patient was sent to the laboratory within 72h, one sample was randomly selected and included in the analysis. Statistical tests were performed without imputation of missing values. P-value < 0.05 was considered statistically significant. Normal distribution was analyzed using Shapiro-Wilk test and q-q analysis. P-value was calculated using Mann-Whitney U-test and Wilcoxon test for nonparametric data where appropriate. Logistic regression was used to obtain odds ratio and Kruskal-Wallis test as multivariate analysis.

38.204 samples were included into the analysis. A total of 1448 cases (3.8%) were tested positive for M. pneumoniae (48.8% females). Baseline characteristics of M. pneumoniae patients are shown in Table 1. Pediatric patients (age ≤ 18 years) represented 75.7% of M. pneumoniae cases and 2.3% of patients were ≥ 60 years of age. 95.0% of M. pneumoniae positive cases were taken from outpatients compared to 78.4% in M. pneumoniae negative cases (MPN) (p < 0.001, OR 0.19 95%-confidence interval (CI): 0.15–0.24) as illustrated in Fig. 1A. M. pneumoniae cases were significantly younger than MPN (median age 11 years (interquartile range (IQR) 8–17) vs. 42 years (IQR 9–65), p < 0.001, OR 0.98, 95%-CI 0.97–0.98). Hospitalized patients with M. pneumoniae were significantly older than outpatients (mean age 17 (IQR 11–40) vs. 11 years (IQR 7–16) in in- vs. outpatients respectively, p < 0.001, OR 1.03, 95% CI 1.01–1.04). We observed differences in age (p = 0.006) and sex (p = 0.04) in M. pneumoniae cases from 2015–2024 (Fig. 1B). In multivariate analysis, young age, year of testing and being an outpatient were associated with a positive M. pneumoniae test (p < 0.001).

Highest incidences of M. pneumoniae were observed in fourth quartile 2015 (16.2%), second quartile 2018 (14.8%) and fourth quartile 2023 (13.4%), while no cases of M. pneumoniae were detected in 2021 (Fig. 1C). Test ordering capacity significantly increased over time (p < 0.001).

Co-infections of M. pneumoniae with bacterial or viral pathogens were frequently detected (21.3%) from 2015–2024. Most common co-infections were influenza A/B, rhinovirus, metapneumovirus and respiratory syncytial virus (supplementary table 1).

Our study highlights the epidemic spread of M. pneumoniae during the winter season 2015 and spring / summer 2018 in Germany. M. pneumoniae re-emergence in 2023/2024 in Germany is comparable to the pre-pandemic number of cases. Cases in the second quartile 2024 were decreasing. In contrast to other bacterial pathogens e.g. Streptococcus pyogenes ([9]), which caused massive outbreaks after the Covid-19 pandemic, current spread of M. pneumoniae has not exceeded the historical number of cases even though testing capacity has dramatically increased over time. Interestingly, most M. pneumoniae patients were young and not hospitalized. Still, hospitalized M. pneumoniae patients were significantly older. This contrasts current data from the Netherlands and Denmark [6, 7] who frequently observed hospitalization and 11% had severe M. pneumoniae CAP which needed treatment in the intensive-care unit. We noticed fluctuating incidences of M. pneumoniae since 2015 corresponding to reported epidemics with M. pneumoniae.

Current empirical treatment of CAP with beta-lactam with or without beta-lactamase-inhibitor is not active for M. pneumoniae. Treatment options include tetracycline, quinolones and macrolides. Addition of a macrolide to empirical treatment of CAP is currently limited by guidelines to severely ill hospitalized patients with CAP. Current treatment algorithms will withhold active antibiotic treatment in most cases as shown by our data as patients were mainly observed in the outpatient setting. Unfortunately, proportions of macrolide-resistant M. pneumoniae are constantly rising and have increased worldwide from 18.2% in 2000 to 76.5% in 2019 [10]. Macrolide resistance is less pronounced in Europe with 5% resistant isolates. On the basis of this data we advise for the implementation of the following interventions a) introduction of a reporting obligation in Germany to early detect epidemics b) adjustment of empirical antimicrobial treatment for in- and outpatients during epidemics of M. pneumoniae and c) the limitation of macrolide use in CAP and other diseases (e.g. sexually transmitted diseases) to microbiologically confirmed or severe cases outside epidemics to avoid evolution of antimicrobial resistance in Germany.

Our data is in line with previously reported epidemics of M. pneumoniae occurring every 3–7 years. The most plausible explanation is that in contrast to many other bacterial infections the adaptive immune system plays a central role for protections. Low Mycoplasma-specific IgG antibodies that are induced during symptomatic infection but not in asymptomatic carriers increase the risk for infection [11, 12]. In contrast, pre-existing high titers of IgG have been shown to be protective of M. pneumoniae infection in non-smokers [11], but titers of IgG decline over time. During the COVID-19 pandemic low numbers of M. pneumoniae cases have been reported [8, 13]. Non-pharmaceutical interventions (NPI) have been shown to be protective of SARS-Cov-2 infection and infection with other respiratory viruses [14] and have also been also protective for M. pneumoniae [13]. Since infections with M. pneumoniae are distributed by droplets like other respiratory viruses and SARS-Cov-2 NPI must have had an effect on M. pneumoniae distribution in the population during COVID-19 pandemic. This might have led to declining antibody titers in the population, increased susceptibility and current M. pneumoniae epidemic in Germany [8].

Furthermore, co-infection was observed in every fifth patient with influenza A/B and rhinovirus being most prevalent. This is in line with a large-scale outbreak in France in 2024. This cohort is characterized by a high number of pediatric outpatients which confirms clinical data on M. pneumoniae CAP to be less severe. Adult patients were the minority of M. pneumoniae cases in most seasons in our cohort. This contrasts recent data from Denmark where 7% of children, 19% of adult patients aged 19–74 years and 48% >75 years were hospitalized over several seasons [6]. M. pneumoniae was reported to be among the five most common pathogens of severe CAP [4]. Current German guidelines on CAP advise against routine testing for M. pneumoniae in adults and children. Therefore, the following hypothesis can be raised which should be targeted by future studies: I) Pediatricians are more aware of M. pneumoniae CAP. II) Adult CAP patients are highly underdiagnosed with M. pneumoniae in Germany.

Our study has some limitations: No information on clinical disease and course of infections was available. Long-term colonization and asymptomatic carriers with M. pneumoniae have been reported, but should then also have been detected during the Covid-19 pandemic. Also, higher bacterial load has been reported in symptomatic patients. We cannot measure the rate of secondary hospitalizations of patients which might have led to an overestimation of outpatients in our cohort. Furthermore, we cannot estimate incidence of M. pneumoniae in all areas of Germany since most patients were localized in the North and/or West of Germany (supplementary Fig. 1). An epidemic situation of M. pneumoniae infections has been reported by adjacent countries in 2023/2024 which suggests generalizability of our results [6, 7]. Detection of pathogens tested outside of the panels described was not included into the analysis. Therefore, the rate of coinfection could be higher, especially during COVID-19 pandemic.

In conclusion, empirical treatment of CAP patients often does not include coverage of M. pneumoniae. Based on a more thorough implementation of available surveillance data into clinical routine, respective therapies could be adapted more quickly during epidemic outbreaks of M. pneumoniae infections. As hospitalization is increased in adult patients and severe courses of disease have been frequently reported, physicians should be aware and test for M. pneumoniae in CAP.

Table 1

Baseline characteristics of *Mycoplasma pneumoniae* positive patients
Baseline characteristics	Total	2015	2016	2017	2018	2019	2020	2021	2022	2023	2024
Total	1448	23	23	44	26	85	61	0	9	485	692
age (median, interquartile range)	11 (8–17)	7.5 (6–26)	24 (11–42)	9 (8-19.5)	14.5 (8.3–43.0)	10.0 (6–14)	10.0 (8–21.0)	na	32.0 (11–39)	10.5 (7–15)	11 (8–17)
age groups years (%) − 0–18 − 19–59 - >59	1090 (75.7)	15 (68.2)	9 (42.9)	30 (69.7)	16 (66.7)	67 (78.8)	44 (74.6)	na	4 (44.4)	387 (80.2)	518 (75.0)
	307 (21.3)	6 (27.3)	9 (42.9)	10 (23.3)	5 (20.8)	15 (17.6)	14 (23.7)	na	4 (44.4)	87 (18.0)	157 (22.8)
	42 (2.3)	1 (4.5)	3 (14.2)	3 (7.0)	3 (12.5)	3 (3.5)	1 (1.6)	na	1 (11.1)	8 (1.7)	15 (2.2)
sex (% females)	690 (47.7)	15 (66.2)	5 (21.7)	19 (43.8)	16 (61.5)	45 (52.9)	24 (39.3)	na	6 (66.7)	244 (50.3)	317 (45.8)
outpatients (%)	1375 (95.0)	22 (95.6)	18 (78.3)	40 (90.9)	22 (84.6)	74 (87.1)	55 (90.2)	na	8 (88.9)	469 (96.7)	667 (96.4)

Acknowledgement

We would like to thank all the colleagues involved in the diagnostic process. We would especially acknowledge Prof. Dr. R. Bialek, Dr. U Zelck, Dr. B. Wölk, Dr. A. Pahl, H. Koch and their teams for their outstanding work and support.

Funding: The authors did not receive support from any organization for the submitted work.

Conflict of interest: The authors have no competing interests to declare that are relevant to the content of this article.

Ethics approval: Approval was obtained from the ethics committee of University hospital Schleswig-Holstein in Luebeck. The procedures used in this study adhere to the tenets of the Declaration of Helsinki (Ethics approval number 2024-897167). Author contributions: Waldeck, Kramer and Rupp made substantial contributions to the conception and design of the work; the acquisition, analysis and interpretation of data. Waldeck and Kramer drafted the work and all authors revised it critically for important intellectual content. Waldeck and Boutin contributed figures and tables. All authors approved the final version of the manuscript.

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No competing interests reported.

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Emergence of Mycoplasma pneumoniae before and after COVID-19 pandemic in Germany

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