Methicillin-resistant Staphylococcus aureus (MRSA) submandibular abscess in a neonate

Abstract

Neonatal suppurative submandibular sialadenitis and abscess formation is an exceedingly rare entity. This report describes a complex case of a male neonate with a methicillin-resistant Staphylococcus aureus (MRSA) submandibular abscess, requiring emergency intubation due to acute airway compromise. The patient was admitted to the paediatric intensive care unit, received appropriate antibiotic treatment and underwent urgent surgical drainage of the abscess. He made a full recovery and remains well 18 months later. No comorbidities or common risk factors for the disease were identified. Although extremely uncommon, neonatal submandibular abscesses can lead to significant morbidity. Neonates tend to present insidiously, and sudden clinical deterioration with airway compromise is possible. MRSA has been increasingly implicated in these infections, even in the absence of relevant risk factors. As such, continued clinical vigilance is essential for prompt diagnosis and prevention of life-threatening complications. Multidisciplinary input is paramount for appropriate management of these complex infections.

Background

Acute suppurative sialadenitis and abscess formation is an uncommon entity in the neonatal period. The solitary or primary involvement of the submandibular gland is exceedingly rare, with less than 50 cases of neonatal suppurative submandibular sialadenitis (NSSS) reported in the literature.¹ Although rare, the condition is associated with significant morbidity and life-threatening complications. As such, a high index of clinical suspicion is required for prompt recognition and management.

This report describes a rare, complex case of a neonate presenting with a Panton-Valentine leucocidin (PVL) positive methicillin-resistant Staphylococcus aureus (MRSA) submandibular abscess requiring emergency intubation and surgical drainage. Relevant previous literature is reviewed and common risk factors, aetiopathogenesis and appropriate management of the condition are discussed.

Case presentation

A 7-day-old male neonate presented to the emergency department with a 1-day history of a large, rapid-onset left neck swelling and reduced breastfeeds. He was born at 37 weeks’ gestation, to a gravida 2 para 2 mother of Asian origin. The delivery was complicated by placenta previa, requiring emergency caesarean section. He had no underlying medical conditions and was discharged home on day 2 of life, after establishing breastfeeds.

On presentation to the emergency department, the patient was apyrexial with a white cell count of 8.6×10⁹/L (normal range: 8.1–20.4×10⁹/L) and a C reactive protein of 56 mg/L (normal range: 0–6 mg/L). Examination revealed a 5×5 cm left-sided submandibular swelling extending to the midline, with overlying erythema and induration of the skin. He was hence commenced on empirical intravenous cefotaxime, gentamicin, amoxicillin and metronidazole for broad-spectrum coverage. The patient was noted to have several apnoeas, initially resolving with airway positioning. However, within hours he deteriorated, with prolonged obstructive apnoeic episodes secondary to extrinsic compression from the neck mass. Due to concerns regarding worsening upper airway obstruction, he was intubated and transferred to the nearest paediatric intensive care unit (PICU).

Investigations

Neck ultrasound performed at the tertiary referral centre was inconclusive, demonstrating appearances in keeping with extensive cellulitis within the anterior and lateral neck subcutaneous soft tissues, but no definite collection for drainage. However, the examination was difficult and provided limited views. An MRI scan was hence undertaken demonstrating a 24×24×17 mm abscess in the left submandibular gland (figure 1). Blood cultures, lumbar puncture results, virology screen (including adenovirus, Epstein-Barr virus, cytomegalovirus, and hepatitis B and C) were all unremarkable. Maternal MRSA screen, including swabs taken from the nose, axilla and groin on admission to hospital prepartum, was negative.

Figure 1.

Axial T1-weighted MRI scans with contrast demonstrating a 24×24×17 mm abscess in the left submandibular gland (A, B).

Treatment

In view of the imaging findings, urgent incision and drainage under general anaesthetic was performed, revealing an abscess cavity containing pus and saliva. Postoperatively, the patient remained intubated in the PICU due to continuing airway concerns, but required no inotropes or vasopressors. He clinically improved over the following 72 hours and was successfully extubated on day 4 of admission. Intraoperative pus samples grew MRSA and intravenous vancomycin was hence commenced, while awaiting PVL results. Reference laboratory testing using whole-genome sequencing later confirmed the presence of the PVL toxin gene, with the isolate belonging to clonal complex (CC) 5, a known community-associated lineage of MRSA; in view of this, the antibiotic regime was converted to linezolid and rifampicin, which continued for 2 weeks. The patient and any family members residing at the same address also received MRSA decolonisation treatment.

Outcome and follow-up

The patient was successfully discharged home following completion of antibiotic treatment. Repeat ultrasound 2 months after discharge demonstrated no anatomical abnormalities. He underwent extended immunological testing on an outpatient basis, which included immunoglobulin levels, lymphocyte phenotyping extended panel, functional antibodies, neutrophil oxidative burst, complement C3/C4 and galactose-1-phosphate uridyl transferase. The results of these were unremarkable, demonstrating no primary immunodeficiency disorder. The patient currently remains healthy, with no developmental concerns or further infections 18 months following initial admission.

Discussion

Salivary gland infection is exceptionally rare in the neonatal period, with the commonest site being the parotid gland. Isolated neonatal submandibular sialadenitis is extremely uncommon, with less than 50 cases reported in the current literature.¹ It has been suggested that the submandibular gland produces more mucous than the parotid, which is bacteriostatic, hence protecting the gland from infection.² Ascending infection from the oral cavity to the salivary glands has been proposed as the likely pathogenesis; however, haematogenous spread or cutaneous entry are also possible.²

The most common causative pathogen of NSSS is S. aureus, although Pseudomonas aeruginosa, Klebsiella pneumoniae and anaerobes have also been isolated in a small number of cases.^3–5 MRSA has been increasingly implicated over the past 20 years, owing to the emergence of antimicrobial resistance. Historically, MRSA has been recognised as a pathogen associated with healthcare settings and predominantly affecting individuals with comorbidities or specific risk factors. However, over the past two decades, the emergence of community-acquired MRSA (CA-MRSA) strains has been noted,⁶ with an increase in the incidence of MRSA head and neck infections among children with no identifiable risk factors.^{7 8} Nosocomial transmission of CA-MRSA strains and hospital outbreaks have also been observed in several countries.⁹ In a longitudinal surveillance of MRSA isolates in the East of England conducted in 2012–2013, CC5 was the third commonest lineage accounting for approximately 5% of the total.¹⁰ Although substantial progress has been achieved in reducing MRSA infections in healthcare settings in the UK, the burden of disease remains high. In 2019–2020, a total of 814 MRSA bacteraemias were reported in England, compared with 2935 in 2008–2009. However, the decline has been most marked in hospital-onset cases, which were targeted by infection control interventions, with community-onset MRSA bacteraemias now accounting for 68% of cases compared with 45% in 2008–2009.¹¹

It is difficult to determine with certainty the origin of infection in our patient. PVL is a toxin most commonly associated with CA-MRSA infections,⁶ and neonatal infections with PVL positive MRSA have been linked to both vertical and nosocomial transmission.^{12 13} While direct invasion from the submandibular gland seems the most likely cause, cutaneous entry, via a small invisible injury in the neck during delivery or hospitalisation, cannot be excluded.

Neonatal submandibular sialadenitis commonly presents with fever, poor oral intake, cervical lymphadenopathy, submandibular swelling and purulent material extruding from Wharton’s duct opening. The condition is associated with potentially life-threatening complications, including abscess formation, septicaemia and airway compromise.¹ The presence of not only pus, but also saliva, in a potential abscess cavity means that rapid swelling and extrinsic compression of the airway can occur, as evident in this case. While adults often present with localising signs and symptoms, children, and especially neonates, tend to have a more insidious presentation, where sudden clinical deterioration is possible.¹⁴

NSSS has been associated with a number of predisposing factors, including prematurity, dehydration, orogastric or nasogastric feeding, poor oral hygiene, congenital anomalies of the floor of mouth as well as immunological deficiencies.^{15 16} The combination of immunological immaturity and presence of bacteria in the oral cavity could explain the increased propensity for sialadenitis in the preterm neonate. The need for enteric feeding is also more common in premature neonates. Prolonged orogastric or nasogastric feeding may result in reflex salivary gland hypostimulation causing a functional blockage of salivary ducts and hence predisposing to infection.¹⁶ It is, however, imperative to appreciate that such infections can occur even in the absence of obvious risk factors, as described in this case. The patient in question was a healthy infant with no history of recent travel abroad, prolonged hospitalisation, enteric feeding, anatomical abnormalities or evidence of immunodeficiency. Maternal infection screen, including MRSA, was unremarkable. A high index of clinical suspicion is hence required, even in atypical cases, in order to instigate timely and appropriate management.

Ultrasound is the first-line imaging modality for all superficial palpable neck masses in the paediatric population, as it allows quick, non-invasive and cost-effective acquisition of information without utilising contrast, radiation or sedation.¹⁷ However, cross-sectional imaging, such as CT or MRI, still comprise the gold standard. Important differential diagnoses in neonates with submandibular masses include lymphadenitis, lymphagioma, teratoma and dermoid cyst.¹

Appropriate antibiotic therapy is key in the management of NSSS. Empirical broad-spectrum antibiotics should be commenced on presentation; these can later be adjusted based on sensitivities, if available. In this case, broad-spectrum antibiotics were rationalised to vancomycin, as the causative pathogen was identified as MRSA. Linezolid and rifampicin were commenced once the PVL toxin was noted to be positive. Antibiotic choice was based on available sensitivities and local guidelines. Linezolid has been shown to inhibit the production of certain staphylococcal toxins, including PVL.¹⁸ It also achieves high penetration into skin and soft tissues with almost 100% oral bioavailability, therefore enabling an intravenous to oral switch and outpatient treatment.^{19 20} In severe PVL MRSA skin and soft tissue infections (SSTIs) using a combination of two or three agents, such as linezolid combined with clindamycin and rifampicin, might be of benefit.²¹ This is based on in vitro synergistic bactericidal effect for antimicrobial combination.^{21 22} Clindamycin was not used in our case due to the presence of resistance.

Alternative treatments options include manual expression of pus from Wharton’s duct or surgical drainage. These, however, are not without risks and should be reserved for severe or progressive infections not responding to antibiotic therapy.²³ Early surgical debridement is very important in severe MRSA SSTIs.²¹ The recent emergence of drug-resistant pathogens has important implications and may necessitate re-evaluation of the overall approach in management. Subspecialist and multidisciplinary input is paramount for appropriate management of these rare and complex infections, in order to minimise morbidity and prevent life-threatening complications.

Learning points.

• Although extremely rare, neonatal submandibular sialadenitis and abscess formation can lead to significant morbidity and life-threatening complications.

• Neonates tend to present insidiously and rapid deterioration with airway compromise can occur.

• A high index of clinical suspicion is required, even in infants lacking obvious risk factors.

• The recent emergence of drug-resistant pathogens has led to an increased incidence of methicillin-resistant Staphylococcus aureus head and neck infections in the paediatric population.

• Subspecialist and multidisciplinary input is paramount for appropriate management of these rare and complex infections.