A Case of Bacteremia-Associated Neck and Mediastinal Abscess

Background

Dialister pneumosintes is a non-spore-forming, non-motile, non-fermentative, gram-negative anaerobic bacilli [1]. It is reported to occur as normal flora in the nasopharynx, oral cavity, intestine, and vagina [2,3]. This bacterium was first detected in 1921 from the nasopharyngeal secretion of patients during the influenza epidemic of 1918–1919, and was initially named Bacterium pneumosintes [4].

We present a case of Dialister pneumosintes-associated mediastinal and neck abscess in a previously healthy young patient who was getting treatment for a possible dental abscess. To the best of our knowledge, this is the first case report of mediastinal and neck abscess caused by this organism.

Case Report

A 30-year-old woman with no significant past medical history presented to the Emergency Department with a 1-day history of fever (38°C), vomiting, and diarrhea. Two weeks prior to admission, she visited her general practitioner for tooth ache, and she was prescribed a 14-day course of oral antibiotic (clarithromycin 500 mg BD) for a suspected dental abscess. On examination, she was tachycardic and febrile, with nontender, non-erythematous generalized swelling of the right side of her face. She had no lymphadenopathy or organomegaly. Her heart sounds were normal, and the chest was clear on auscultation.

Initial investigations showed neutrophilic leucocytosis (white blood cell 29.06×109/liter, reference value 4.00–11.00×109/liter; neutrophil 27.55×109/liter, reference value 2.00–7.00×109/liter) with high C-reactive protein (154 milligram/liter, reference value <11 milligram/liter) and lactate (3 millimole/liter). Her chest radiograph was normal (Figure 1). Considering the raised inflammatory marker and septic presentation, she was started on intravenous piperacillin and tazobactam (4.5 grams TDS) combination antibiotic. After 48 hours of initiation of broad-spectrum antibiotic, she was still having intermittent high-grade fever. Preliminary blood and stool cultures grew no organism.

After that, she was re-evaluated and an urgent CT scan of the neck-thorax-abdomen-pelvis was performed, which detected a septated, peripherally enhancing, anterior mediastinal abscess measuring 5.5×3.2×6 cm in transverse, antero-posterior, and craniocaudal dimensions, respectively, with extension into the lower neck up to the level of the thyroid gland (Figure 2A, 2B). An X-ray orthopantomogram showed lucency around the lower premolar tooth, in keeping with the clinical suspicion of abscess formation (Figure 3). Given the CT scan finding, while waiting for the incision and drainage, parenteral metronidazole (500 milligram TDS) was added, as advised by the microbiologist.

Therefore, urgent referrals were sent to the Maxillofacial, ENT, and Cardio-thoracic Departments of the affiliated university hospital. After inter-departmental discussion, the patient was transferred under the ENT specialty. An emergency incision and drainage of the mediastinal and neck abscess was performed under general anesthesia. The procedure was complicated by massive hemorrhage. Suturing of the bleeding point was attempted without success owing to its unidentified source. Bleeding was controlled conservatively with pressure dressing. Major hemorrhage protocol was activated, and she was transfused with 7 units of red blood cells and 7 units of fresh frozen plasma. She was transferred to the Intensive Therapeutic Unit (ITU), where she remained intubated for 3 postoperative days.

Her pus sample was sent for culture and sensitivity. Auramine stain of pus was negative for acid-fast bacilli. Both aerobic and anaerobic cultures of the pus, including the culture for Mycobacterium tuberculosis, were sterile. Gram film of the pus sample showed profuse leucocytes. Pus polymerase chain reaction (PCR) testing for Mycobacterium tuberculosis and Mycobacterium avium complex were negative. Her HIV test result was also negative. However, PCR testing of pus detected 16s rRNA gene, suggestive of gram-negative anaerobic bacilli.

Gradually, she was stepped down from the ITU. A post-procedure CT angiogram of the neck and thoracic area detected thrombus inside and surrounding the right internal jugular vein, suggestive of an intra-operative bleeding site, and acute pulmonary embolism in the right-side lobar branch of the pulmonary artery. It also revealed minimal residual collection of pus in the right supraclavicular space extending into the right superior mediastinum. Hence, she was treated with subcutaneous low-molecular-weight heparin (LMWH), which was later changed to oral anticoagulant (edoxaban 30 milligram OD).

Although her inflammatory markers were decreasing, she remained tachycardic with intermittent episodic high temperature. After discussion with the microbiologist, her antibiotics were changed to meropenem (1 gram iv TDS), vancomycin (1 gram iv BD), and oral fluconazole (50 milligram OD). On her seventh postoperative day, she developed swelling of her right upper limb due to deep vein thrombosis of her upper limb veins revealed by compression venography.

Eventually, one of her initial anaerobic blood culture sample, which was sent on the day of her admission, grew Dialister pneumosintes. Her antibiotic was changed to amoxicillin plus clavulanic acid (1.2 grams TDS) and metronidazole (500 milli-grams TDS). Her inflammatory markers gradually came down. A repeat CT scan of her neck and thorax showed reduction in the amount of collection in the right supraclavicular fossa and superior mediastinum. She remained clinically well and afebrile. At the time of hospital discharge, she was prescribed a further 21-day course of oral antibiotic amoxicillin with clavulanic acid (625 milligrams TDS) and metronidazole (400 milligrams TDS).

A follow-up ultrasound scan, which was done 2 weeks after her discharge, showed absence of any residual collection in the neck. Four weeks later, she was seen in the Outpatient Department, where she reported she was feeling significantly better. At present, she is waiting for Venous Thromboembolism (VTE) Clinic follow-up.

Discussion

Initially, we were unable to identify the source of infection due to non-specific presentation of symptoms and signs. Computed tomography revealed a mediastinal and neck abscess, and an orthopantomogram revealed a dental abscess. However, there was no evidence of descending transmission of infection from the orthodontic source. In this case, it was a hematogenous spread of infection from the dental abscess, and Dialister pneumosintes bacteremia of periodontal origin has been documented in the literature [5,6]. A study of 135 systemically healthy dentistry patients revealed D. pneumosintes was the pathogenic organism in 83% of cases of severe periodontitis and 19% of cases of slight periodontitis [7]. We were unable to confirm that D. pneumosintes was the pathogenic organism causing her tooth infection, as we did not cultivate any specimen or aspirate from her tooth. Based on the characteristics of the pathogen and the nature of the infection, and with the absence of any other source, it is likely that the neck and mediastinal abscess was due to bacteremia from a periodontal infection.

Currently, there are 4 known species in Dialister genus, consisting of 135 strains; however, D. pneumosintes and D. micraerophilus are commonly encountered species [8]. D. pneumosintes is difficult to grow in the conventional culture media and the 16s rRNA-based PCR assay has been developed for the detection of this pathogen [9]. This microorganism has been isolated from periodontitis [7], gingivitis, root canal infection [10], sub-gingival plaque [9], human bite wound infection [11], respiratory tract, head and neck infection [3], and vaginal infection [12]. Severe infective complications have been reported, including brain abscess [13] and liver abscess [5] with a suspected dental source of origin.

Our patient developed pulmonary embolism and internal jugular vein (IJV) thrombosis following a major bleed during the intervention owing to injury to the IJV. Her pre-operative CT scan was not suggestive of any thrombosis. Two cases have been reported as D. pneumosintes bacteremia-associated thrombosis. The first was suppurative thrombosis of ovarian vein in a young woman [12] and the second case was cavernous sinus thrombosis in an immunocompromised elderly woman in association with other anaerobes [14].

The mortality rate of patients with mediastinitis is up to 40% despite aggressive treatment with broad-spectrum antibiotics [15]. Frequently isolated organisms in culture of the deep neck and mediastinal infection are Streptococcus, Bacteroides, Staphylococcus, Peptostreptococcus, Pseudomonas, E. coli, Klebsiella, and H. influenzae [16]. Deep neck and mediastinal abscess are rare complications of dental abscess, which demand urgent surgical intervention with antibiotic treatment.

Conclusions

Both immunocompetent and immunocompromised individuals can be affected by Dialister pneumosintes. Patients who present with tooth ache who have been prescribed antibiotics need appropriate follow-up to monitor the response to therapy or any development of complications. Likewise, patients with septic presentation with a history of dental infection and who are not responding to antibiotic treatment needs urgent imaging to assess for presence of a deep-seated abscess. Due to the high mortality rate, an emergency surgical approach is necessary once the diagnosis of mediastinal abscess is confirmed.