08.02 ID
08.02 Infectious disease [PDF link] – bacterial infections: Leptospirosis, Leprosy, Lyme disease, Pseudomonas aeruginosa, Mycoplasma pneumoniae, Q fever, Staphylococci (Staph aureus / S. aureus), MRSA, Toxic shock syndrome, Tetanus, Other clostridia
More on Staph aureus bacteraemia
Not high yield for med school but clinically important – Staph aureus bacteraemia carries high mortality (up to 30%).
History and clinical examination
Essentially trying to identify if there is a specific source for infection (eg prosthetic devices, endocarditis, abscess, etc)
Look specifically for peripheral stigmata of endocarditis
Neurological examination at baseline ± further Ax as neurological deficits may develop
Further investigations
Blood cultures – should be repeated every 24-48h until clearance is demonstrated
Transthoracic echocardiogram – looking for evidence of endocarditis
If concerns for vertebral osteomyelitis or psoas abscess (eg back pain), CT/MRI spine can be performed
Management: (1) source control, (2) antimicrobial treatment
Source control, eg removal of prosthetic devices. As early as possible.
Antimicrobial treatment – empirically treating for MRSA then targeted when sensitivities available
Always check local trust guidelines. Always IV initially.
Vancomycin is usually used as first line – loading dose + maintenance. Check troughs and adjust dosing as needed.
Methicillin-sensitive Staph aureus (MSSA) – a penicillin of some sort is used. In the trust I’ve worked at, the choice was usually flucloxacillin IV 2g every 6h, but other penicillins such as nafcillin or oxacillin are used as well.
Penicillin allergy: use vancomycin
Methicillin-resistant Staph aureus (MRSA) – continue vancomycin.
Complicated vs uncomplicated bacteraemia
Uncomplicated bacteraemia is defined as
Clearance of bacteraemia within 4 days of onset of effective antimicrobial therapy, AND
Defervescence (no more fever) within 72h of onset of effective antimicrobial therapy, AND
No implanted prostheses, endocarditis or other metastatic sites of infection.
Complicated bacteraemia is any Staph aureus bacteraemia that does not fulfil above criteria
Duration of antibiotic treatment
Uncomplicated: Continue IV antimicrobial therapy for 14 days after clearance of bacteraemia
Complicated – depends on source control, site/extent of infection, and clinical judgment.
Usually minimum of 28 days of antibiotic treatment, of which at least the initial 14 days should be IV therapy
Links: SAPG website has a good summary.
Interesting articles
Example of targetoid rash and presentation of Mycoplasma pneumoniae. Lu H, Zhang B. Mycoplasma-Induced Rash and Mucositis. N Engl J Med 2023;389:1601–1601. https://doi.org/10.1056/NEJMicm2305301.
One of the differentials I thought of when reading this article was Kawasaki’s disease. Reminder that Mycoplasma pneumoniae may be a differential as up to 25% can present with mucocutaneous disease. Another differential would be SJS, especially if associated with recent medication changes.
