Streptococcus oralis meningitis in pregnancy

Abstract

While pregnancy is a time of relative immunosuppression, infective endocarditis and bacterial meningitis remain rare. We present a case of a pregnant woman with Streptococcus oralis endocarditis and meningitis. This is the first reported case of Streptococcus oralis meningitis in a patient without predisposing risk factors. This case highlights the importance of collecting blood cultures in febrile illness during pregnancy and illustrates that effective management plans can be formulated without performing invasive diagnostic tests such as transesophageal echocardiography.

Introduction

Bacterial meningitis is rare during pregnancy but associated with high morbidity and mortality. ¹ We describe a case of an atypical presentation of bacterial meningitis in pregnancy, and to the best of our knowledge, the first report of Streptococcus oralis meningitis in a patient without predisposing risk factors such as immunosuppression, invasive surgical procedures or spinal anaesthesia.

Case report

A 33-year-old woman presented to our hospital at 36 weeks of gestation with a five-day history of diarrhoea, vomiting, fever, myalgia and transient painful red spots on her fingers. On examination, she had good oral hygiene, vesicular breath sounds audible throughout both lung fields, no heart murmurs, nor peripheral stigmata of endocarditis. A gravid uterus was palpable with no abdominal tenderness. Blood test abnormalities included mild lymphopenia of 0.8 × 10⁹/L, CRP 74 mg/L and creatinine 97 µmol/L.

She had been diagnosed with intrahepatic cholestasis in a previous pregnancy; consequently, bile acids were being monitored during her current pregnancy. Other than previous history of gallstone pancreatitis and cholecystectomy two months after her initial pregnancy and delivery, she was fit and well. She gave a history of possible penicillin allergy.

An initial diagnosis of viral infection, possibly COVID-19, was made and a septic screen was sent including urine microscopy, chest radiograph, blood cultures and SARS-CoV2 PCR. Other conditions considered included gastroenteritis, urinary tract infection and rarer conditions such as listeriosis. The history of erythematous painful lesions on her fingers suggested Osler's nodes. Antibiotics were not immediately started as she was clinically stable without any signs of sepsis. The SARS-CoV2 polymerase chain reaction (PCR) was negative, but the first blood culture was positive for Gram-positive cocci and she was commenced on vancomycin and gentamicin for suspected infective endocarditis. Three blood cultures subsequently grew Streptococcus oralis. Transthoracic echocardiography (TTE) did not demonstrate evidence of vegetation or valvular dysfunction, but treatment was continued for possible infective endocarditis given the history of Osler's nodes, fevers and a typical organism grown on blood culture as per Duke's clinical criteria for infective endocarditis.

Three days after the initial presentation, she developed a frontal headache with visual disturbance and confused speech. Computed tomography imaging of her brain was normal, and lumbar puncture revealed turbid cerebrospinal fluid (CSF) with a white cell count of 550 × 10⁶/L (28% polymorphs), protein 3.34 g/L and glucose 0.1 mmol/L. No organisms were seen on Gram stain and the CSF remained sterile; subsequent amplification of the 16s rRNA gene confirmed the presence of Streptococcus mitis group (which contains S. oralis) DNA. Her antibiotic regimen was switched to intravenous ceftriaxone, to cover both meningitis and suspected endocarditis. Magnetic resonance imaging (MRI) of her brain with angiography showed pyogenic ventriculitis on a background of generalised meningitis, without mycotic aneurysms or embolic disease. This was managed conservatively following a discussion with the neurosurgical team.

The patient made a steady recovery with resolution of her neurological symptoms within 24 h. Serum bile acids rose to 158 µmol/L on day 6 of admission so labour was induced, and followed by vaginal delivery of a healthy baby. She was discharged home to complete a four-week course of ceftriaxone via the Outpatient Parenteral Antibiotic Treatment service. A follow-up MRI brain demonstrated improvement of the ventriculitis.

Discussion

There is modulation of the immune system during pregnancy, due to immunosuppressive cytokines produced by the placenta and fetus, which can cause differing susceptibility to pathogens. However, B cell immunity remains unchanged. Bacterial meningitis is rare during pregnancy with the most common causative organisms being Streptococcus pneumoniae (52%) and Listeria monocytogenes (16%). This condition is associated with considerable morbidity and mortality for both mother and fetus, including miscarriage in the first trimester. ¹

Streptococcus oralis is a member of the viridans group of streptococci and is a normal component of the oral and pharyngeal microbiota. Although it is an organism of low virulence, it is capable of opportunistic pathogenicity and phenotypic variation. As with other oral bacteria, it can enter the bloodstream during daily activities such as tooth brushing and flossing, as well as during invasive dental procedures and oral surgery. It is rapidly cleared by the immune system, but it can cause systemic disease, typically endocarditis. ²

S. oralis is a relatively common cause of bacterial endocarditis, but a very rare cause of meningitis. ² Transesophageal echocardiography (TOE) may be performed in patients with a high clinical suspicion of endocarditis and a non-diagnostic TTE but is an invasive procedure that would not have changed the management of this case.

Case studies of S. oralis meningitis have been described in immunocompromised individuals, due to malignancy ³ or alcohol dependency, ² and as complications of neurosurgical procedures, ⁴ oral surgery and spinal anaesthesia. ⁵ Meningitis is also a recognised neurological sequelae of infective endocarditis. ² 16S PCR is a pan-bacterial molecular diagnostic test, with proven utility in identifying causative organisms in culture-negative infections from samples obtained from typically sterile sites. This technology allowed us to prove the aetiology of our patient's meningitis.

This case illustrates the importance of collecting blood cultures in pregnancy-related febrile illness, as it confirmed bacteraemia and highlighted the causative organism. This case also shows the role of 16S PCR sequencing in diagnostics; this is not a very sensitive test for CSF, but allowed us to confirm S. oralis as the cause of her meningitis.

Lastly, while TOE may be indicated in patients with a clinical suspicion of endocarditis, with a non-diagnostic TTE but a typical organism on blood cultures and indicative clinical features, our case demonstrates that effective management plans can be formulated without this invasive procedure.