Microbiology
Infections
Question 14 of 77
A 65 year old man presents to ED with a fever and a 24 hour history of a red, hot, swollen painful knee which he is reluctant to move due to pain. Bloods show an elevated WCC and CRP. Joint aspiration demonstrates the presence of Gram-positive cocci. Which of the following antibiotics is most appropriate to start in this patient:
Answer:
The most common cause of septic arthritis is Staphylococcus aureus, which is consistent with a finding of Gram-positive cocci. The first line treatment of septic arthritis is with intravenous flucloxacillin. Clindamycin may be used in penicillin allergic patients, and vancomycin or teicoplanin in suspected MRSA. If gonococcal arthritis or Gram-negative infection suspected, cefotaxime or ceftriaxone would be indicated.Septic Arthritis
Microbiology / Infections
Last Updated: 21st April 2019
Infective Agents
- Staphylococcus aureus (most common)
- Streptococcus pyogenes
- Haemophilus influenzae
- Neisseria gonorrhoeae
- Pseudomonas aeruginosa
- Enterobacteriaceae
Pathogenesis
- Haematogenous spread - distant infection causes bacteraemia and subsequent septic arthritis
- Direct infection - trauma, surgery or a deep ulcer can infect an adjacent joint
Risk factors:
- Elderly
- Diabetes mellitus
- IV drug user
- Recent joint surgery
- Immunocompromised
- Endocarditis or recent bacteraemia
- Prosthetic or damaged joints (knee most commonly affected)
Clinical Disease
- Acute onset of painful, swollen, hot, erythematous joint with reduced range of movement secondary to pain +/- systemic features
Diagnosis
- Joint aspiration for Gram stain, M, C & S
- Cloudy or purulent joint fluid, raised WCC (usually > 50,000), neutrophilia, low glucose and Gram-stain may suggest infection that can be confirmed by culture or NAAT
- Blood cultures
- X-ray may show periarticular soft-tissue swelling
Treatment
- Immobilise joint and start physiotherapy early
- Antibiotic therapy
- Flucloxacillin first line (suggested duration of treatment 4 – 6 weeks, longer if infection complicated).
- If penicillin allergic, clindamycin
- If MRSA suspected, vancomycin or teicoplanin
- If gonococcal arthritis or Gram-negative infection suspected, cefotaxime or ceftriaxone
- Surgical therapy
- Aspiration and irrigation of joint to reduce inflammatory damage
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
