Invasive pneumococcal disease with widespread metastatic involvement in a healthy adult: a case report

Abstract

Background

This was an unusual case of invasive pneumococcal disease in an immunocompetent adult without serious underlying medical conditions. Streptococcus pneumoniae bacteraemia was found with multiple distant sites of infection, including polyarticular septic arthritis, osteomyelitis, multi-level spondylodiscitis, and paravertebral, psoas and pelvic abscesses.

Case presentation

A fit and well 56 year old woman presented with a 10 day history of fevers, rigors, and multiple hot, swollen, tender joints. Septic arthritis was initially thought unlikely, but when blood tests showed marked inflammatory response and the patient was febrile, joint aspiration was performed. Streptococcus pneumoniae was grown from blood cultures and aspirates from multiple joints. MRI confirmed distant sites of infection including left sacroiliac joint osteomyelitis, multi-level spondylodiscitis, and small paravertebral, psoas and pelvic abscesses, which were not amenable to drainage. The patient completed 11 weeks of antibiotic therapy, with IV Amoxicillin followed by IV Ceftriaxone, and made a good recovery with full resolution of joint disease. The patient had obesity but was not in a recognised risk group for invasive pneumococcal disease. No underlying medical conditions were found that would predispose her to such widespread infection.

Conclusions

Septic arthritis can be polyarticular. Urgent joint aspiration and blood cultures should be undertaken for any patient in whom septic arthritis is considered. Patients with invasive pneumococcal disease should be investigated for predisposing risk factors and should be adequately immunised. This case provides a timely reminder of the virulence of pneumococcus, the severity of invasive pneumococcal disease, and the importance of vaccination.

Background

Streptococcus pneumoniae is a common coloniser of the upper respiratory tract and may lead to a broad range of infections, from relatively mild conditions such as sinusitis or otitis media to life-threatening invasive diseases like invasive pneumococcal disease (IDP); it remains a significant cause of morbidity and mortality on a global scale [1]. Septic arthritis is an uncommon clinical feature, occurring in less than 2% of adult patients with S.pneumoniae bacteraemia [2]. IPD usually occurs in patients at the extremes of age (less than 5 and over 65 years) or in those with significant underlying organ dysfunction or impaired immunity [3].

We present an unusual case of IPD with multiple distant sites of infection including polyarticular septic arthritis in an immunocompetent adult without serious underlying medical conditions. Our case provides a useful reminder of the importance of urgent joint aspiration if there is a possibility of septic arthritis, even in the presence of polyarticular symptoms, and also that cases of IPD without apparent risk factors should be appropriately investigated for predisposing conditions.

Case presentation

A usually fit and well 56-year old woman presented to hospital unable to weight bear due to worsening joint swelling and pain. Ten days prior she had sudden onset of vomiting and rigors followed by left knee pain and swelling, with gradual involvement of multiple other large and small joints. There was no history of recent respiratory symptoms or diarrhoea. She was Scottish and had a body mass index (BMI) of 38 kg/m², which is classed as obese. She had never smoked cigarettes and there was no history of recurrent infections, symptoms suggestive of sleep apnoea, excess alcohol intake, previous hospital admissions or recent significant travel.

On initial assessment by paramedics, she was found to be febrile, with a temperature of 38.9 °C. On admission to hospital observations were as follows: respiratory rate 18/minute, oxygen saturations 96% on air, heart rate 123/minute, blood pressure 124/77 mmHg, temperature 37.8 °C. On examination heart sounds were normal, chest was clear and abdomen was soft and non-tender. There was erythema, swelling and reduced range of movement of both knees, both shoulders, the left ankle and left middle finger.

The initial blood tests showed a marked inflammatory response, with white blood cells 30.2 × 10⁹/L (4.0–11.0), neutrophils 26.2 × 10⁹/L (2.0-7.5) and C-reactive protein 403.9 mg/L (0.0–10.0). The x-ray of the left knee showed suprapatellar effusion and two small lytic lesions of the patella in keeping with infective changes. Chest x-ray showed left basal linear atelectasis with lung fields otherwise clear.

The initial clinical impression was that of an inflammatory or reactive arthritis. Septic arthritis was only considered when the patient’s clinical condition worsened and she developed fever of 39.1 °C. An aspirate from the left knee joint was performed 12 h after admission, yielding turbid synovial fluid, with many white blood cells and Gram-positive cocci on microscopy. Intravenous (IV) Vancomycin was started prior to surgical intervention. The patient underwent multiple washouts, including arthroscopic washouts of the left knee on days 1 and 2 and of the right knee on day 2, open washouts of the left middle finger on days 1 and 2, and an open washout of the left ankle on day 6. A computed tomography (CT) of the chest, abdomen and pelvis with contrast found inflammation of the left psoas and left proximal thigh without an abscess.

Two sets of blood cultures obtained on the day of admission flagged positive for Streptococcus pneumoniae after 12 and 15 h of incubation, respectively. The patient was switched to high dose IV Amoxicillin (2 g 4-hourly) on day 3, and subsequently to IV Ceftriaxone 2 g OD on day 7. S. pneumoniae was also isolated from joint aspirates from both knees and the left ankle, and from pus from the left middle finger. Micrococcus luteus was isolated from one theatre sample (left ankle aspirate) but was considered clinically insignificant. Blood cultures taken on day 2 of admission had no growth.

Given the multiple metastatic foci of infection, magnetic resonance imaging (MRI) of whole spine and transthoracic echocardiography (TTE) were requested to investigate for deep sites of infection. There were no vegetations seen on TTE. The MRI of whole spine showed multifocal changes of spondylodiscitis in cervical, thoracic and lumbar spine, osteomyelitis of the left sacroiliac joint, and multiple abscesses (small paravertebral, left psoas and pelvic). Interestingly, the patient did not have back pain at any point of her illness. The abscesses were not amenable to drainage by either neurosurgery or interventional radiology.

The final diagnosis was invasive pneumococcal disease with polyarthritis, multifocal spondylodiscitis, left psoas and pelvic abscesses. Joint pains and fever settled, and she remained in hospital for inpatient rehabilitation. After five weeks of treatment, a whole-spine MRI showed slight reduction in the size of collections and no new areas of disease. She was discharged home on day 39 of admission to continue IV Ceftriaxone via PICC line under the Outpatient Hospital Antibiotic Team. A repeat MRI at ten weeks demonstrated complete resolution of the collections, and she completed a total of 11 weeks of antibiotics. At three-month follow-up, she was asymptomatic with no residual joint pain.

Undiagnosed underlying immunosuppression or serious underlying medical conditions were considered given the presentation, although none was found despite thorough investigation. Congenital or acquired immunodeficiencies (B & T cell, phagocytic & complement disorders), and haematologic malignancies (including multiple myeloma, lymphoma & leukaemia) were ruled out. Full blood count, immunoglobulins and protein electrophoresis were all within normal range and urinary Bence Jones protein was negative. There was slightly elevated C3 at 1.99 g/L (0.75–1.65) that was consistent with acute phase response, and C4 was within normal range. Imaging revealed no evidence of splenomegaly or malignancy. HIV test was negative. Diabetes mellitus was excluded based upon HbA1c of 42 mmol/mol ( < = 48 mmol/l) and absence of hyperglycaemic symptoms. There was no evidence of chronic renal failure or nephrotic syndrome. The patient was of Scottish ethnicity, and therefore testing for haemoglobinopathies including sickle cell disease was not performed. A screen for autoimmune diseases (Anti-PR3, Anti-MPO, CCP & Connective Tissue Disease screen) was negative.

The patient had not been previously vaccinated against pneumococcus. The patient received a dose of the Pneumovax 23 vaccine (PPV23) during admission, and almost four months later pneumococcal antibody was 154.80 mg/l (> 20.0).

Discussion and conclusions

Our case highlights the importance of considering the possibility of septic arthritis and performing urgent joint aspiration, even in patients with polyarticular symptoms. Any patient with a hot, swollen and tender joint (or joints) should be regarded as having septic arthritis ‘until proven otherwise’ [4] irrespective of any pre-existing joint disease. Diagnostic confirmation requires joint aspiration of synovial fluid for culture, but given that the majority of cases occur by haematogenous spread, blood cultures should also be taken [5]. Septic arthritis is relatively uncommon, with an annual incidence of 5–10/100,000 in the UK [6]. If not promptly recognized, septic arthritis can result in substantial morbidity and mortality, underscoring the importance of maintaining a high index of clinical suspicion [7, 8]. Polyarticular involvement occurs in only 15% of cases [9, 10], which may contribute to a delay in diagnosis.

Several reports suggest that pneumococcal septic arthritis is more likely to involve multiple joints. Ross et al. reviewed 108 cases of pneumococcal septic arthritis in adults and found that 36% had polyarticular disease [11]. The majority of adult cases occurred in individuals with underlying conditions, most commonly rheumatoid arthritis or alcoholism, while only 15% of patients were otherwise healthy. Approximately half of patients had an underlying extra-articular focus, most frequently pneumonia, meningitis, or endocarditis. Notably, there were no reported cases with concurrent psoas or pelvic abscesses or multi-focal discitis.

Another particular aspect of this case was the fact that patient was not in a recognised risk group for developing IPD. Even in the absence of obvious predisposing conditions, patients should be thoroughly evaluated to ensure that potential risk factors are not overlooked [2]. The patient presented in this case report worked in school as a playgroup assistant, which may have led to increased exposure to Streptococcus pneumoniae. We elected to vaccinate the patient with the pneumococcal polysaccharide vaccine (PPV23), both as part of an immunological work up and in an attempt to prevent further episodes of IPD, as it should be ensured that cases of IPD have been appropriately immunised [12].

The primary virulence factor of pneumococci is the polysaccharide capsule, which is also the main target of current vaccines [1]. In the UK, the Joint Committee on Vaccination and Immunisation has recommended vaccination with PPV23 for at risk groups since 1992 and for all adults aged 65 years and over since 2003. This year a switch to using the pneumococcal conjugate vaccine (PCV20) is planned, as this seems to result in longer lasting immunity [12]. This brings the UK closer to current practice in the United States of America, where the Centers for Disease Control and the Advisory Committee on Immunization Practices advise pneumococcal conjugate vaccine (either PCV20 or PCV21) for at risk groups and all adults aged ≥ 50 years. In 2024 the age was lowered from 65 years old for a number of reasons, including that there is a substantial burden of pneumococcal disease in this age group, especially in Black/African American adults where an earlier disease peak is seen [13].

Obesity is not considered to be an at risk condition for pneumococcal disease requiring vaccination in either the UK or the United States, but there is emerging evidence to suggest that this group is at increased risk of IPD and therefore may benefit from vaccination [14]. This would be a significant undertaking given that a significant proportion of adults in the UK are classified as obese; in Scotland 31% of adults were living with obesity in 2024 [15].

Pneumococcal conjugate vaccines are also used in routine childhood immunisation schedules; in the UK, a two-dose schedule of PCV13 is given - at 16 weeks and one year of age. This has been highly effective at reducing childhood pneumococcal disease [16], and has also reduced rates of IPD in adults via indirect methods, although this is partially offset by an increase in non-vaccine-type disease [17]. There has been declining rates of childhood vaccinations in the last decade; in 2023–2024 in England none of the vaccines in the routine childhood schedule met the 95% target set by the World Health Organisation and is required for herd immunity [18]. This raises the possibility of a future resurgence of pneumococcal disease in both adults and children, and our case provides a timely reminder of the virulence of pneumococcal disease and the importance of vaccination.

The strength of this case is that the patient was thoroughly investigated to exclude underlying causes that would predispose to IPD. A limitation is that although we identified that the patient had a high BMI in the obese range, which has been suggested by some studies to increase the risk of IPD, it remains unclear whether this was a contributing factor.

In conclusion, this was an unusual case of IPD with multiple metastatic foci in an immunocompetent adult without serious underlying medical conditions. It provides a useful reminder that septic arthritis can be polyarticular and that, if considered a possibility, joint aspiration should be performed without delay and blood cultures should also be taken. The presence of multiple metastatic foci in Streptococcus pneumoniae bacteraemia should prompt the evaluation of deep-seated infection, and all cases of IPD should be reviewed for underlying risk factors and immunised appropriately. This case also highlights the severity of IPD and the importance of immunisation, at a time of declining childhood vaccination rates.

Abbreviations

BMI

Body mass index

IPD

Invasive pneumococcal disease

PCV13

Pneumococcal conjugate vaccine

PCV20

Pneumococcal conjugate vaccine

PCV 21

Pneumococcal conjugate vaccine

PPV23

Polysaccharide vaccine

IV

Intravenous

MRI

Magnetic resonance imaging

TTE

Transthoracic echo

Author contributions

All authors have approved the manuscript and agree with its submission to BMC Infectious Diseases. S.F. wrote the main manuscript text and D.M. reviewed the manuscript.

Funding

Publication costs were supported by Ninewells Hospital. The funder had no role in study design, data collection, analysis, or manuscript preparation.

Data availability

Data sharing is not applicable to this article as no datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Written informed consent for publication was obtained from the patient.

Competing interests

The authors declare no competing interests.