ABSTRACT
After the use of facemasks, other isolation measures enacted during the SARS-CoV-2 pandemic were lifted, respiratory pathogens, such as RSV, reappeared, but until the November 2023 WHO alert for China, M. pneumoniae had virtually disappeared. After observing a similar reappearance in our hospital, a retrospective analysis of the number of positive M. pneumoniae tests. Between 2018 and December 2023, 1619 PCR tests were ordered and 43 (2.6%) of them were positive. Two outbreaks, one in 2018 and one in 2023, accounted for the majority of cases. Tests were usually ordered in an outpatient setting (53.54%, n = 23) and most of them were paediatric patients with a mean age (sd) of 10.2 (6.2) years. As for the severity of the cases, in the 2018 outbreak, of 15 children who tested positive, 53.3% (n = 8) were admitted to the ward and 6.7% (n = 1) at the intensive care unit. Whereas in 2023, 2 patients were tested in the ward (10.5%) and one in the intensive care unit (5.2%) from a total of 19 patients. The positive rate in 2023 was significantly higher in comparison with years 2020, 2021 and 2022 and significantly lower in comparison with 2018 (P-value=0.003). The outbreak in late 2023 can be explained by the seasonality of Mycoplasma pneumonia alone, which has shown outbreaks every 3–5 years, and it does not appear to be more severe than the previous one.
SARS-CoV-2 pandemic changed the aetiological landscape of community acquired pneumonia. The pandemic-related non-pharmacological measures temporarily impacted the seasonality of respiratory pathogens such as RSV or influenza [Citation1]. Interestingly, Mycoplasma pneumoniae had not yet reappeared, despite the pandemic restrictive measures long been lifted in most of the countries worldwide [Citation2].
In late 2023, the WHO issued an alert of a rising number of cases of paediatric community acquired pneumonia (CAP) cases in China, with M. pneumoniae being one of the agents isolated [Citation3]. In the last weeks of November 23, we have observed an increase in the number of cases of paediatric CAP due to M. pneumoniae in our hospital, so we aimed to analyse the recent epidemiology of M. pneumoniae in our setting, looking at the nasopharyngeal PCR tests/results performed in our hospital in the last 5 years.
From Jan 2018 to Dec 2023, 1619 PCR determinations of M. pneumoniae tests were ordered and 43 of them (2.6%) came back positive. PCR for atypical bacteria which includes M. pneumoniae, Chlamydophila pneumoniae, and Bordetella pertussis is only performed at the physician’s discretion in our centre, based on suggestive clinical picture or course. A multiplex real-time polymerase chain reaction method (Allplex™ Respiratory Panel 4 (Seegene, Corea)) was used. According to the total number of cases and percentage of positive results (, and Table 1 in Appendix), two outbreaks, one in 2018 and another in 2023, accounted for the majority of cases. Eighteen cases were detected in 2018, which represented 41.86% of the cases in the five-year period and a positivity rate of 5.79% in the first semester and 12.96% in the second one. In 2023, 20 cases were detected, which accounted for 46.51% of the cases with a positivity rate of 0.40% in the first trimester and 10.55% in the second one. Positivity ratio rates between the years 2018−2022 and 2023 were computed, and counted data were evaluated using Fisher’s exact test. The positive rate in 2023 was significantly higher in comparison with years 2020, 2021, and 2022; and significantly lower in comparison with 2018 (P-value = 0.003).
Figure 1. Total number of positive cases by semester (green line) and % of positive cases over total tests requested by semester (red line) from 2018 to 2023.
Tests were usually ordered in outpatient settings (53.49%, n = 23) and most of them occurred in paediatric patients with a mean age (sd) of 10.2 (6.2) years. With regard to the paediatric patients, 53.3% (n = 8) were admitted to the ward and 6.7% (n = 1) at the intensive care unit during the 2018 outbreak. In 2023, 19 paediatric patients have been recorded, 2 patients were tested in the ward (10.5%), and one in the intensive care unit (5.2%). All of them recovered after treatment. So, despite the fears that this outbreak could be more severe due to the lack of exposure to M. pneumoniae [Citation4], our data suggest otherwise.
The outbreak we are witnessing in our centre in late 2023 may be explained by the usual seasonality of M. pneumoniae alone, which has shown outbreaks every 3–5 years [Citation5]. Although the outbreak is ongoing, the severity of the cases collected so far does not seem to have increased, and the response to the usual therapy has been the norm in all cases, with complete recovery. As specified in the results, most tests were ordered in outpatient settings so we infer that the severity of most cases ranges from moderate to mild. Our centre is a third-level hospital from the region of Galicia in North West Spain and the reference centre for paediatric infectious diseases in the region, so, although only the cases from one centre were considered, not only were cases from the neighbouring area treated in the area but also referrals from the nearby secondary and first level hospitals. Nevertheless, results should be considered carefully as it is a monocentric study. The severity of the Chinese outbreak might be explained as their protective measures were lifted later and it happened at the same time as the resurgence of other pathogens in the country such as RSV in a population with immunity debt [Citation6]. This increase in M. pneumoniae cases may be occurring in other countries, outlining the importance of enlarging the index of suspicion, particularly in paediatric patients with atypical pneumonia.
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FM-T acted as the principal investigator in randomized controlled trials of Ablynx, Abbot, Seqirus, Sanofi Pasteur MSD, Sanofi Pasteur, Cubist, Wyeth, Merck, Pfizer, Roche, Regeneron, Jansen, Medimmune, Novavax, Novartis, and GSK, with honoraria paid to his institution. FM-T reports a relationship with GSK Vaccines SRL that includes consulting or advisory. FM-T reports a relationship with Pfizer Inc. that includes consulting or advisory. FM-T reports a relationship with Sanofi Pasteur Inc. that includes consulting or advisory. FM-T reports a relationship with Janssen Pharmaceuticals Inc. that includes consulting or advisory. FM-T reports a relationship with MSD that includes consulting or advisory. FM-T reports a relationship with Seqirus Pty Ltd that includes consulting or advisory. The remaining authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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References
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