Mycoplasma pneumoniae and Chlamydia pneumoniae Community-Acquired Pneumonia in Young Adults from a Family Medicine Practice

Abstract

Introduction: A major area of pathology in primary care practice is represented by respiratory infections, from common colds to severe lower respiratory tract illness. Our aim was to evaluate the incidence of Mycoplasma pneumoniae and Chlamydia pneumoniae pneumonia among the patients with suspected atypical pneumonia from a family medicine urban setting in Iași, Romania, to study serological retrospective diagnosis, the therapeutic outcome and the modified immunologic parameters in a subgroup of patients. Methods: We enrolled 93 patients with suspected atypical community-acquired pneumonia (CAP); enzyme-linked immunosorbent assay (ELISA) testing for Mycoplasma pneumoniae and Chlamydia pneumoniae was performed, both immunoglobulins M and G being determined. Considering the systemic inflammation associated to atypical germs infections, in a subgroup of 13 patients, with positive results for Mycoplasma and Chlamydia pneumoniae, interleukin 5, interleukin 8, tumor necrosis factor α and interferon γ levels were determined, using chemiluminescence method (EI-CLA). Results: Positive IgM serology for atypical germs was recorded in 25.8% of patients. Mycoplasma pneumoniae infection was confirmed in 10.8% of patients, Chlamydia pneumoniae infection in 6.5% of patients, and co-infection (both Mycoplasma pneumoniae and Chlamydia pneumoniae) in 8.6% of patients. A number of 41 patients (44.0%) presented chronic cough/bronchial hyperreactivity despite the treatment. Modified values were recorded for all immunological parameters tested, confirming the role in chronic airway inflammation. Conclusions: Mycoplasma and Chlamydia pneumoniae CAP, frequent among young adults, is successfully treated with macrolides, still, the residual symptoms and the modified immunologic parameters need further studies regarding chronic inflammation.

Introduction

Over the last decades, a constant increase has been reported in the prevalence of community-1acquired pneumonia (CAP) determined by Mycoplasma pneumoniae and/or Chlamydia pneumoniae in young adults [1] and a decrease in incidence of pneumococcal pneumonia, due to a better standard of life, especially in the developed countries.

Atypical CAP is usually mild; the incidence of acute infection is highly dependent on collective immunity, the epidemic tendency of occurrence evolving lately towards an endemic profile. A study conducted in an ambulatory setting in Canada, 2005, identified M. pneumoniae and C. pneumoniae as main pathogens in the etiology of CAP [2]. After 1995, the incidence of atypical pneumonia followed a cyclical pattern, with epidemic peaks occurring at intervals of 4-7 years, influenced by herd immunity and living conditions [1,2]. The decline in pneumococcal infections due to vaccination has emphasized the role of atypical pathogens as significant causes of community-acquired pneumonia, particularly among young populations in high-density settings [1,3]. The microorganisms included in the atypical pneumonia group induce constitutional symptoms, upper and lower respiratory tract involvement and can have a protracted clinical course with gradual resolution. The lack of typical findings of lobar consolidation on chest Xray, failure to isolate a pathogen with use of routine bacteriologic testing methods, and lack of response to penicillin therapy are also common features of this group of microorganisms [3]. Risk factors include age (school-aged child, adolescent, young adult), boarding schools, closed communities, smoking and various immune deficiencies. Atypical lower respiratory tract infection is referred to as „walking pneumonia”, due to the gradual onset, mild clinical picture and moderate fever.

Mycoplasma pneumoniae spreads through microscopic droplets, which, once inhaled, attach to the respiratory epithelium, inducing ciliostasis and alteration of the epithelial barrier [4]. Recently, the ADP-ribosylating and vacuolating cytotoxin has been identified (community-acquired respiratory distress syndrome toxin) produced by M. pneumoniae, highly immunogenic and cytopathogenic. This toxin binds to cells in a similar way to pertussis toxin, determining the chronic cough symptoms [4]. A T cell-mediated immune response is responsible for the pathogenesis, as well as various cytokines, including tumor necrosis factor alpha (TNFα), and the pro-inflammatory interleukins (IL)-5, IL8, IL-13 [5,6,7], generating low response in γ interferon (IFNγ) production [7]. Chlamydia pneumoniae can survive for a long time in the airway cells; chronic infection may be linked to the asthma onset [8]. This prolonged survival is correlated with altered production of the protective SPLUNC1 protein in the atopic population [9]. The elevated eosinophil cationic protein levels found in the serum of patients with M. pneumoniae infection may be associated with damage to the respiratory epithelium and accelerated hypersensitivity in the respiratory system [10].

The golden standard in diagnosis is RT-PCR testing, but retrospective etiology can also be confirmed by serology using ELISA method, valid and accessible. In adults, the immunoglobulins M (IgM) response can be reduced, even absent, with high titers of immunoglobulins G (IgG) in the case of recurrence [5,11].

Our aim was to evaluate the incidence of atypical pneumonia in young adults from an urban setting in Iasi, Romania, confirming the role of M. pneumoniae and C. pneumoniae as major pathogens in the ambulatory treated CAP, as well as to assess their impact in the spectrum of respiratory tract infections (RTI) in the postpandemic era. The incidence of atypical bacteria may be related to modified immune markers in some patients leading to long-term consequences influenced by chronic inflammation.

Methods

The study was conducted at a family medicine clinic from Iaşi, Romania, that registers 2630 patients from urban environment, between January 2024 and May 2024. We enrolled 93 patients aged between 15 and 30 years, with suspected atypical pneumonia at presentation, defined by a cluster of signs and symptoms: malaise, moderate fever, headache, sore throat, progressive cough and extra-pulmonary symptoms [12]. The exclusion criteria included confirmed bacterial CAP, viral infection, such as SARS-CoV-2 or influenza, contacts of Bordetella pertussis cases, tuberculosis, severe concomitant diseases (immunosuppression), nosocomial infection, recent steroid therapy or systemic antibiotic treatment two weeks prior to the study entry. The patients were excluded based on medical data charts (e.g., previous conditions) and primary investigations. The informed consent approved by the ethics board was obtained from the participants.

At presentation, we recorded the demographics of each patient, as well as the time from the onset, previous history of RTIs and/or asthma and allergies, smoking status and living conditions. We charted the symptoms and their progression from the onset to presentation, as well as the clinical findings. The CURB65 score was performed in all patients to evaluate the pneumonia severity. None of the patients were hospitalized.

Laboratory samples were obtained, including venous blood specimens for complete blood count, erythrocyte sedimentation rate, C-reactive protein, fibrinogen, liver enzymes and creatinine level. The patients suspected of atypical pneumonia underwent radiological examination for exclusion of lobar pneumonia. Serum samples for the assay of antibodies against M. pneumoniae and C. pneumoniae were obtained at 14 days from presentation. Specific IgM antibodies usually appear within about 1 week after onset of clinical illness, reach peak titers during the third week. The optimal moment of serological confirmation of diagnosis using a single probe must be determined yet [11]. Moreover, definition of what value should be considered as a positive test result has not been definitively established [11].

Infection with Mycoplasma pneumoniae or Chlamydia pneumoniae was confirmed in a retrospective manner in patients tested for specific IgM and IgG. Positive IgM titer has been interpreted as recent acute infection and as confirmation of atypical germ infection. Since adults with reinfection may not present a detectable IgM titer [10,13], a high IgG response (higher than the cutoff provided by the manufacturer) was considered marker of previous infection with atypical germs but was not useful in confirming the current episode.

IgM and IgG antibodies for M. pneumoniae and C. pneumoniae were determined using enzyme-linked immunosorbent assay (NovaLisa TM, NOVATEC Immunodiagnostic GMBH, Peru). Results were recorded in accordance with the manufacturers' instructions (positive results over 11 NTU – NovaTech Units, signifying titer higher than the cutoff, grey-area between 9-11 NTUs and negative – lower than 9 NTUs). All samples used double pair technique, with predetermined negative control, cut-off control and positive control; specificity is over 95%, and sensitivity is 83.3%.

In a subgroup of 13 patients, with positive IgM serology (high titers) for Mycoplasma and Chlamydia pneumoniae, IL-5, IL-8, TNFα and IFNγ levels were determined, using chemiluminescence method (EI-CLA), as markers of the systemic inflammatory response.

For all suspected CAP patients with the exception of COVID-19, in light of better outcomes with the earliest possible interventions, the Infectious Diseases Society of America recommends initial empiric antimicrobial therapy until laboratory results can be obtained to guide more specific therapy [14]. The patients with suspected atypical pneumonia received treatment with clarithromycin 500 mg bid for 7 days. In case of persistent or aggravating symptoms (over 48 hours), the regimen was switched to moxifloxacin 400 mg daily for 7 days, according to the guidelines. The patients presenting residual bronchial hyperreactivity (BHR) lasting more than 8 weeks received montelukast 10 mg daily for a period of 3 months. Clinical response was evaluated at 48 hours, 14 days (after completion of treatment), 4 and 8 weeks and will be monitored every 3 months for a period of one year, both short term response as well as the possible recurrence being recorded.

Results

The age distribution in the atypical pneumonia group varied between 15 and 30 years of age, with a mean of 24.6 years. Sex distribution showed prevalence of females (62.3%). Analysis of data regarding self-reported date of onset revealed that 67.1% of patients presented in less than seven days from the onset of symptoms. The mean duration of symptoms at presentation was 5.2 days. Most patients attended school or university and lived in students’ dormitories.

Evaluation for atypical bacterial infections

In our tested group, M. pneumoniae infection was confirmed in 10.8% of patients (n=10), C. pneumoniae infection in 6.5% of patients (n=6), and co-infection (both M. pneumoniae and C. pneumoniae) was present in 8.6% of patients (n=8). IgM positive serology for atypical germs infection was recorded in 24 patients (25.8%). Of the 93 patients tested for atypical germs, 58.1% (n=54) presented positive titers for IgM and/or IgG (

Table 1. Serology results using ELISA in patients with suspected atypical community-acquired pneumonia.

	Number of cases	%
Ig M positive titers of which:	24	25.8
Mycoplasma pneumoniae IgM	10	10.8
Chlamydia pneumoniae IgM	6	6.5
M. pneumoniae and C. pneumoniae IgM (co-infection)	8	8.6
Ig G positive titers of which:	30	32.3
Mycoplasma pneumoniae IgG	13	14.0
Chlamydia pneumoniae IgG	8	8.6
M. pneumoniae and C. pneumoniae IgG (co-infection)	9	9.7
Negative titers	39	41.9

). Previous infection (IgG positive titers was confirmed in 30 patients (32.3%), 14.0% (n=13) for Mycoplasma pneumoniae, 8.6% (n=8) for Chlamydia pneumoniae and 9.7% both IgG titers present (n=9) – Table 1.

Treatment results and follow-up

The clinical remission rate after treatment (clarithromycin 500 mg bid or moxifloxacin 400 mg daily) was 90.3%. A number of 41 patients (44.08%) presented prolonged cough or BHR that lasted more than 8 weeks from the onset. The spirometry was performed for these cases indicating obstructive pattern in 25 cases. Only 16 patients from this subgroup tested positive for respiratory allergens. Most of them presented a personal history of atopic conditions and 19 of this group had positive titers for Mycoplasma or Chlamydia pneumoniae. This group received treatment with montelukast, 10 mg daily, for up to 3 months or inhaled corticosteroids in case of confirmed atopy.

Immune markers tested in the atypical pneumonia group

We summarize these results in

Table 2. Levels of immune markers tested in a subgroup of patients with atypical pneumonia.

	Normal range values as provided by the manufacturer	Results below normal range (no. of cases)	Results in the normal range (no. of cases)	Results above the normal range (no. of cases)
TNFα	1-8.1 pg/mL		6	7
IFNγ	2-2.7 pg/mL	6	3	4
IL-5	3.5-5 pg/mL	4	5	4
IL-8	3.5-5 pg/mL		6	7

TNFα – tumor necrosis factor alpha; IFNγ – interferon gamma; IL – interleukin.

. We may notice an increase in the level of TNFα in 7 patients, low value for interferon γ in 6 patients, high levels of IL-5 and IL-8 in 4 and respectively 7 patients. We may correlate the high levels of TNFα, IL-5 and IL-8 and the low levels of IFNγ with the previous atypical germ infections.

Discussion

The distribution of cases during the study interval is mostly endemic. Most patients described a progressive onset that could mimic a viral infection, which sometimes delays the visit to the doctor’s office. The cough, one of the major symptoms, has an impact on regular activities, associating frequently chest pain and headache. The clinical picture includes also malaise, low-grade fever, sore throat; the late inspiratory crackles identified on lung auscultation are useful in raising the suspicion of atypical pneumonia in the absence of other signs commonly found in pneumococcal pneumonia [15].

The number of patients testing positive shows a high incidence of atypical pneumonia in the young adults’ group of age which correlates with the data from literature. In our tested group, the positive results for M. pneumoniae (10.8%) are higher than for C. pneumoniae (6.5%). The total percentage of patients diagnosed with atypical germs infection is 25.8%; most authors report percentages ranging from 24% to 58% positive results on ELISA determination for atypical germs [16,17]. An interesting finding is the high percentage of patients with co-infection (8.6%), testing positive for both germs, clinical picture being quite similar to mono-infection. Hence, the possibility of cross-reactivity has to be established. Wu et al. acknowledge that in adults where IgM response can be absent, for the M. pneumoniae IgM−/IgG+ subgroup of a study, a single serum MP-IgG level of ≥92.67 RU/mL can be used as a reference criterion for the diagnosis of acute M. pneumoniae infection [18]. Since the values of this claim depend on the manufacturer specific recommendation, we avoided considering the IgM-/IgG+ patients as acute infection cases.

The incidence of atypical pathogens currently identified highlights the post-COVID-19 resurgence of Mycoplasma pneumoniae and Chlamydia pneumoniae infections, particularly in Europe and Asia [19]. This increase is attributed to the decline in herd immunity accumulated during the pandemic, as well as the biological characteristics of these pathogens, such as cytoadherence and toxin synthesis, further exacerbated by environmental factors like fine particulate matter (PM2.5) and NO₂ pollution [19].

The high clinical response rate to clarithromycin therapy demonstrates that, despite the emergence of resistant Mycoplasma pneumoniae strains [1,20], macrolide (ML) remains the first-line treatment for atypical pneumonia due to their proven efficacy. The strict relationship between ML use and development of M. pneumoniae resistance is strongly supported by the evidence that the incidence of resistance is greater in the countries with the most extensive ML consumption such as the East Asia [14]. Data collected in Europe seem to indicate that the level of resistance is relatively lower. In Germany, repeated evaluations during the last 20 years have shown that rate of resistance was no higher than 3.9% [11]. Moreover, even in mild to moderate cases, ML resistance can cause CAP with persistent clinical symptoms, prolonged hospital stay, more relevant radiological findings, and greater risk of extra respiratory complications [11]. The increasing prevalence of antimicrobial resistance underscores the need for cautious use of macrolides and the development of alternative therapeutic strategies to effectively manage the resurgence of these infections.

M. pneumoniae suppresses IFNγ production, a pivotal factor in the evolution of BHR, contributing to immune evasion, while Chlamydia pneumoniae modulates apoptosis, extending host cell longevity and enabling its persistence within the respiratory epithelium [21]. Prolonged cough and bronchial hyperreactivity occurred in 44% of patients within the study group. Residual cough improved in all cases treated with montelukast, since it is related to persistent inflammation of airways. The relationship between M. pneumoniae and C. pneumoniae infection and asthma is already confirmed. Patients with asthma having a higher chance of infection due to the low levels of SPLUNC1 protein, involved in the bacterial clearance [22,23]. At the same time, both M. pneumoniae and C. pneumoniae have a role in the dysregulation of the TH₂ lymphocyte activity. Not all infected patients develop asthma, but some individuals can be genetically predisposed to the chronic effects of infection and present higher risk of infection [22,23]. Modified levels of IL-5, IL-8,

TNFα and IFNγ in our tested subgroup of patients has limited value due to the small sample size but opens new perspectives of study regarding inflammatory mechanisms connected to atypical germs infection.

The study has several limitations, including the small sample size, reliance on retrospective serological diagnosis without molecular methods such as RT-PCR, and the single-center design, which limits the generalizability of the findings. In addition, the short follow-up period prevents a complete assessment of long-term outcomes such as symptom recurrence or chronic inflammation. Future studies should focus on larger, multicenter cohorts and incorporate advanced diagnostic tools to improve applicability in primary care settings.

Conclusions

CAP determined by M. pneumoniae and C. pneumoniae is frequent among the young adult population attending school and university, with M. pneumoniae infection rates higher than those for C. pneumoniae infection. Despite the mild clinical picture, cough is the most aggressive symptom. Most cases respond to macrolide treatment, but recurrence and residual airway hyperreactivity is commonly found in the study population. Modified levels of cytokines determined in a subgroup revealed the link between atypical germs infection and persistent inflammation of the airways.