Severe empyema caused by mixed oral anaerobic bacterial infection: a case report

Introduction

Empyema is a purulent infection caused by the accumulation of purulent exudate in the pleural cavity, which can be life-threatening. Pathogens typically originate from pulmonary infection foci, thoracic or mediastinal lesions (1). Common causative organisms include aerobic bacteria such as Streptococcus pneumoniae, Staphylococcus aureus, Klebsiella pneumoniae, Haemophilus influenzae, and anaerobic bacteria. Conventional culture methods easily miss anaerobic bacteria, which often cause putrid empyema (2). The human oral microecosystem is complex, with over 700 microbial species identified, including various opportunistic pathogens (3). These microbial communities usually maintain dynamic equilibrium with the host, but when this balance is disrupted, local oral infections can occur and potentially disseminate systemically, leading to multi-organ infectious diseases (4,5).

Recent studies have demonstrated the significant role of the oral microbiome in respiratory health and diseases. The oral cavity directly connects with the upper respiratory tract, facilitating potential transit of oral microorganisms into the respiratory system (6). Oral dysbiosis caused by poor oral hygiene can lead to various oral diseases and has been increasingly recognized for its association with respiratory diseases and their pathogenesis (7). Ectopic abscesses caused by oral anaerobic bacterial infections are clinically rare and easily misdiagnosed or overlooked. Recent applications of high-throughput sequencing technology in pathogenic microorganism detection have brought new opportunities for precise diagnosis and treatment of such complex infections. This case provides a detailed analysis of the diagnostic and therapeutic process of severe empyema caused by mixed oral anaerobic bacterial infection, aiming to enhance clinicians’ understanding of ectopic infections caused by oral pathogens. We present this article in accordance with the CARE reporting checklist (available at https://acr.amegroups.com/article/view/10.21037/acr-2025-181/rc).

Case presentation

Patient information

An 80-year-old male with poor oral hygiene and multiple dental caries, with a medical history of hypertension, coronary heart disease, and leukopenia, had not received regular treatment previously.

Clinical presentation

The patient was admitted with “left-sided chest pain with chills and fever for 4 hours”. Upon admission, his temperature was 38.3 ℃, accompanied by chills without rigors, left-sided chest pain of unclear nature, no referred pain to the left upper extremity or left facial region, no obvious cough or expectoration, and no nausea or vomiting.

Physical examination

Vital signs: temperature 38.3 ℃, pulse 103 bpm, respiratory rate 24 breaths/min, blood pressure 144/79 mmHg, oxygen saturation 97% (room air). The patient was conscious but appeared lethargic, with no cyanosis of lips and diminished breath sounds over the left lung.

Diagnostic workup and treatment course

The complete timeline of clinical events, diagnostic findings, interventions, and outcomes is summarized in Table 1.

Day 1 laboratory results: white blood cell count 3.72×10⁹/L, neutrophil percentage 75.50%, lymphocyte percentage 19.00%, lymphocyte count 0.71×10⁹/L, hemoglobin 108 g/L, platelet count 187×10⁹/L, high-sensitivity C-reactive protein 78.35 mg/L, interleukin-6 1,206.4 pg/mL, procalcitonin 13.41 ng/mL. Chest computed tomography (CT) showed left pleural effusion with interlobar fissure involvement and left lower lobe atelectasis, with localized calcification of coronary and major vessel walls (Figure 1A). Serial chest CT images documenting disease progression and treatment response are presented in Figure 1.

Figure 1 Chest CT images of the same anatomical plane before and after treatment. (A) Admission chest CT: left pleural effusion with interlobar fissure involvement and left lower lobe atelectasis. (B) Day 2 with worsening chest pain, repeat chest CT before closed drainage: multiple loculated left pleural effusions with left lower lobe atelectasis, progression from previous imaging. (C) Post-thoracoscopic surgery chest CT: multiple loculated left pleural effusions with left lower lobe atelectasis showing post-drainage changes with reduced effusion. (D) Discharge chest CT: loculated left pleural effusion with left lower lobe atelectasis post-surgery, reduced effusion compared to previous imaging, improvement in left lung patchy shadows. CT, computed tomography.

On day 2, the patient developed worsening chest pain, and a repeat chest CT revealed multiple loculated left pleural effusions (Figure 1B). Ultrasound-guided left thoracic closed drainage was performed, followed by intrathoracic hemorrhage. The patient subsequently underwent thoracoscopic empyema debridement, thoracoscopic pleural adhesiolysis, thoracoscopic cavity incision and hemostasis, and thoracoscopic examination. Post-thoracoscopic surgery chest CT showed improvement with reduced effusion (Figure 1C). Excised fibrous tissue showed suppurative inflammation with fibrinous necrosis and coagulated tissue on pathological examination (Figure 2).

Figure 2 Postoperative tissue pathology: suppurative inflammation with fibrinous necrosis and coagulated tissue (hematoxylin and eosin staining, ×200).

Next-generation sequencing (NGS) results from surgically excised tissue: Finegoldia magna (sequence count 249, moderate pathogenic grade), Epstein-Barr virus (sequence count 208,118, strong pathogenic grade), human herpesvirus 6 (sequence count 32,684, strong pathogenic grade).

Pleural fluid culture showed no bacterial growth. Pleural fluid NGS results: Porphyromonas gingivalis (sequence count 2,427,897, strong pathogenic grade), Prevotella intermedia (sequence count 253,891, strong pathogenic grade), Fusobacterium nucleatum (sequence count 210,979, strong pathogenic grade), Finegoldia magna (sequence count 982, moderate pathogenic grade).

Treatment outcome

Based on NGS results, the patient received meropenem plus metronidazole for anti-infective therapy and ganciclovir for antiviral treatment. On day 11, repeat laboratory tests showed: white blood cell count 3.43×10⁹/L, neutrophil percentage 53.50%, lymphocyte percentage 32.9%, hemoglobin 89 g/L, platelet count 255×10⁹/L, high-sensitivity C-reactive protein 36.81 mg/L, procalcitonin 0.57 ng/mL. Repeat chest CT showed improvement in left lung lesions with reduced effusion. At discharge, chest CT demonstrated further improvement with loculated left pleural effusion and left lower lobe atelectasis post-surgery, showing reduced effusion compared to previous imaging (Figure 1D). The patient’s temperature normalized, and appetite and physical strength improved. He was discharged and continued oral amoxicillin-clavulanate plus metronidazole for sequential therapy. Two-month follow-up showed good recovery.

Patient perspective

The patient expressed gratitude for the rapid diagnosis and treatment. He stated that the chest pain was severe and frightening, but the medical team’s prompt intervention provided relief. The patient acknowledged that his poor oral hygiene may have contributed to the condition and committed to better dental care in the future.

Ethical statement

All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

Clinical characteristics and diagnostic-therapeutic process analysis

This case involves an 80-year-old male with long-term poor oral hygiene, existing oral infectious foci including dental caries, underlying diseases such as hypertension and coronary heart disease, and compromised immune function. The patient presented primarily with fever and left-sided chest pain, with imaging revealing left-sided empyema. Notably, the patient lacked obvious respiratory symptoms such as cough and expectoration, which may be related to the unique pathogenic characteristics of the causative organisms. Oral anaerobic bacteria such as P. gingivalis typically cause chronic infections with relatively insidious onset (8). When pathogens migrate from the oral cavity to the thoracic cavity, they may only present with non-specific symptoms such as fever and chest pain without obvious cough or expectoration, easily leading to missed or misdiagnosis.

Recent studies have highlighted the increasing recognition of empyema caused by oral anaerobic bacteria. A case series reported severe pneumonia with empyema due to multiple anaerobic infections, where metagenomic NGS identified various oral anaerobic bacteria in bronchoalveolar lavage (BAL) fluid, blood, and pleural effusion (9). Another pediatric case series identified oral obligate anaerobes represented by Parvimonas micra and Porphyromonas gingivalis in children with pneumonia and empyema, emphasizing that these pathogens are often overlooked in pediatric populations (10). The microbiology of pleural infections shows that strictly anaerobic bacteria are found in 12.8% of all culture-positive cases and in 17.8% of community-acquired infections alone (11).

Oral anaerobic bacterial infections leading to oral diseases are positively correlated with pneumonia risk and pneumonia-related mortality. A prospective study by Hata et al. included 39 pneumonia patients who underwent bronchoscopic examination and oral hygiene evaluation, showing that patients with total oral hygiene scores ≥5 had significantly increased numbers of specific anaerobic bacteria detected in the lungs (12). However, thoracic infections caused by oral anaerobic bacteria are relatively rare in clinical practice. Therefore, for patients with obviously poor oral hygiene who present with unexplained chest pain and fever, empyema should be suspected, and active etiological examination should be performed for definitive diagnosis.

After confirming the diagnosis of empyema, rapid identification of causative pathogens is crucial for guiding anti-infective therapy. This case employed NGS to detect pleural fluid and intraoperative purulent cavity tissue, identifying multiple oral anaerobic bacteria including P. gingivalis, P. intermedia, F. nucleatum, and F. magna, providing evidence for targeted antibiotic selection. NGS performs high-throughput sequencing of DNA and RNA in samples, offering advantages including broad detection range, high sensitivity, and quantitative capability (13). Research by Huang et al. demonstrated that NGS detection accuracy and sensitivity for bronchoscopic samples were significantly superior to traditional methods, enabling rapid diagnosis and guiding precision treatment (14). Chen et al. further confirmed that NGS analysis of BAL samples could reveal respiratory microbiome changes in patients with different underlying diseases, providing more precise diagnostic information (15). This demonstrates the unique advantages of NGS in microbiological pathogen diagnosis, particularly for complex infectious diseases caused by rare, difficult-to-culture, or mixed infections.

Treatment of severe empyema requires close collaboration between medical and surgical teams. After definitive diagnosis, this patient initially underwent thoracic closed drainage, but developed intrathoracic hemorrhage post-drainage, followed by thoracoscopic surgery to clear purulent cavity fluid, excise fibrous tissue, drain pus, and control infection. Medically, the anti-infective regimen was promptly adjusted based on NGS results, selecting drugs targeting anaerobic bacteria (16). Through coordinated medical and surgical treatment, the patient’s infection was effectively controlled with good outcomes. Multiple studies have shown that empyema patients receiving thoracoscopic surgery have better prognosis than those receiving closed drainage alone. A randomized controlled study by Hoque et al. comparing chest tube drainage and video-assisted thoracoscopic surgery (VATS) in acute empyema found that the VATS group had shorter hospital stays (16.05 vs. 25.78 days, P<0.001) and lower complication rates (42.5% vs. 77.5%) (17). Research by Nayak et al. showed that empyema patients receiving surgical treatment (including VATS) had significantly lower in-hospital mortality and 30-day, 6-month, and 1-year mortality rates compared to those receiving chest tube drainage alone (18). Early surgical intervention helps thoroughly clear purulent cavities and control infection foci, and when combined with medical antimicrobial therapy, can significantly improve prognosis and reduce mortality (19). This case fully demonstrates the importance of medical-surgical collaboration in treating severe empyema.

Association between oral microecological imbalance and systemic diseases

The oral cavity is an important portal of the human body, and oral microecology is closely related to overall health. The oral microbiome is a complex ecosystem consisting of bacteria, fungi, archaea, and viruses that contribute to oral health (20). The oral cavity contains hundreds of microbial species that normally maintain dynamic equilibrium with the host. However, when factors such as poor oral hygiene and decreased immunity lead to microecological imbalance, opportunistic pathogens can proliferate abnormally, causing oral infections. More importantly, oral infections are not limited to the oral cavity but can predispose individuals to various systemic diseases, with respiratory infections being particularly common (21).

Son et al. analyzed data from 122,251 participants in a Korean cohort database and found that the greater the number of dental caries and missing teeth, the significantly higher the risk of pneumonia, with oral health status and oral hygiene behaviors being associated with pneumonia (22). Zhou et al. conducted a case-control analysis of 60 chronic obstructive pulmonary disease patients with periodontitis (case group) and 60 patients with normal lung function and periodontitis (control group), finding that chronic obstructive pulmonary disease patients with periodontitis showed worse periodontal conditions compared to those with normal lung function (23). Berg et al. conducted longitudinal monitoring of pneumonia incidence for up to 1 year in dental patients from the Marshfield Clinic Health System, using time-to-event analysis and proportional hazards models to investigate relative pneumonia risk over time in groups with poor oral health, showing that poor oral health significantly increased pneumonia risk (24).

This demonstrates that good oral health is particularly important, especially for high-risk groups such as the elderly and immunocompromised individuals. Regular oral examinations and timely detection and treatment of dental caries, periodontitis, and other oral diseases help maintain oral microecological balance and prevent abnormal proliferation and dissemination of oral pathogens (25). Yang et al. conducted a 12-year follow-up study of 49,400 patients with chronic periodontitis, finding that patients receiving periodontal treatment had significantly lower pneumonia risk compared to the general population (26). Ribeiro et al. implemented routine dental care interventions for intensive care unit (ICU) patients and found that regular dental care interventions focusing on oral hygiene and periodontal treatment for critically ill patients could significantly reduce ICU mortality (27).

Therefore, strengthening public oral health education and improving oral healthcare awareness is crucial. Particularly for high-risk groups such as elderly individuals and chronic disease patients, targeted health education and management should be implemented. Additionally, for infectious diseases of unknown origin, oral infection should be considered, and etiological examination should be actively performed for definitive diagnosis. This case of severe empyema once again warns us that oral health cannot be neglected, and strengthening oral management is urgent.

Future applications of NGS technology in complex infectious disease diagnosis and treatment

NGS technology demonstrates unique advantages in etiological diagnosis of infectious diseases. Compared to traditional bacterial culture and polymerase chain reaction (PCR) detection, it offers characteristics including a broad detection range, high sensitivity, and quantitative capability. NGS can detect almost all known pathogenic microorganisms, including bacteria, viruses, fungi, parasites, and some rare, difficult-to-culture pathogens. Retrospective studies show that the overall clinical sensitivity and specificity of NGS are 50.7% and 85.7%, respectively, while those of standard diagnosis are 35.2% and 89.1%, respectively (28). Ivy et al. analyzed numerous prosthetic joint fluids using NGS and found that compared to paired cultures, NGS identified additional microorganisms in 8% of culture-positive cases and detected microorganisms in 31% of culture-negative cases (29). Additionally, NGS can discover new, unknown pathogens, playing a unique role in infectious disease outbreaks and emerging diseases.

For patients after antimicrobial therapy, NGS demonstrates high sensitivity through dynamic monitoring of pathogen changes, especially when traditional culture methods have low positive rates. Recent studies have shown promising results in applying NGS for respiratory tract infections. Lai et al. demonstrated that metagenomic NGS identified 76.8% true-positive cases in patients with lower respiratory tract infections, significantly outperforming traditional culture methods (30).

NGS technology is playing an increasingly important role in the diagnosis and treatment of infectious diseases. With decreasing detection costs, establishment of standardized guidelines, database improvement, and development of multi-omics integrated analysis strategies, NGS is expected to become an important tool for routine etiological diagnosis of infectious diseases, leading the development of precision medicine in infectious diseases. Recent advances have shown the integration of artificial intelligence and machine learning algorithms into NGS workflows, significantly improving genomic data analysis speed, accuracy, and efficiency (31).

Conclusions

Through analysis and discussion of this case of severe empyema caused by oral anaerobic bacterial infection, we systematically elucidated the intrinsic relationship between oral microecology and systemic diseases, demonstrated the application potential of NGS technology in complex infectious disease diagnosis and treatment, and provided new insights for research and prevention of related diseases. With the deep application of new technologies such as multi-omics big data and artificial intelligence in the medical field, precision prevention, diagnosis, and treatment of infectious diseases will usher in a bright future.

Acknowledgments

We thank the patient for providing consent for publication of this case report. We also acknowledge the laboratory staff for their technical assistance in NGS analysis and the surgical team for their excellent patient care.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://acr.amegroups.com/article/view/10.21037/acr-2025-181/rc

Peer Review File: Available at https://acr.amegroups.com/article/view/10.21037/acr-2025-181/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://acr.amegroups.com/article/view/10.21037/acr-2025-181/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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