MicrobiologyTier 1Medical Sciences concept

Peritoneal dialysis peritonitis - causative organisms

Core concept

Route	Organisms
Touch contamination (commonest)	Coagulase-negative staphylococci - the single commonest isolate
Exit-site / tunnel infection	Staph aureus, Pseudomonas aeruginosa
Transmural / enteric	E. coli, Klebsiella, Enterococcus, anaerobes
Haematogenous	Streptococci, Staph aureus
Environmental / water	Fungi (Candida), non-tuberculous mycobacteria

Gram-positives dominate overall (~50-60%)
Multiple organisms, or enteric Gram-negatives plus anaerobes, point to SECONDARY peritonitis from a perforated viscus -> urgent CT and surgical opinion
- Pure single-organism Gram-positive growth is almost always PD-related; polymicrobial enteric growth is a surgical problem until disproved
Culture-negative peritonitis (target <15%) - prior antibiotics, fastidious organisms, or poor technique; send large-volume effluent (50 mL) in blood culture bottles

Diagnosis - 2 of 3 (ISPD 2022)

Clinical features - abdominal pain and/or cloudy effluent
Effluent WCC >100/microL (0.1 x10^9/L) after a dwell of >=2 h, with >50% polymorphs
Positive Gram stain or culture

In APD with rapid cycling, use the >50% polymorph proportion, not the absolute count - a short dwell dilutes it
Normal effluent WCC is <8/microL
Eosinophilic effluent - allergy to icodextrin or catheter material, fungal, or resolving peritonitis

Presentation

Feature	Frequency
Cloudy effluent	~84%
Abdominal pain	~79-88%
Nausea/vomiting	~31-51%
Fever >37.5C	~29-53% - often absent; do not use fever to exclude it
Hypotension	~18%

Empirical treatment

Intraperitoneal is the preferred route (higher local levels) unless the patient is septic - then IV
Cover both: Gram-positive with vancomycin or a first-generation cephalosporin, Gram-negative with a third-generation cephalosporin or an aminoglycoside
Duration 2 weeks for most; 3 weeks for Staph aureus, Pseudomonas, enterococci, or relapsing disease
Adjunctive oral N-acetylcysteine to mitigate aminoglycoside ototoxicity (2022 recommendation)
Fungal peritonitis -> remove the catheter immediately plus antifungal; do not attempt to treat through it

Catheter removal indications: refractory peritonitis (no improvement by day 5), relapsing peritonitis, fungal, refractory exit-site/tunnel infection, mycobacterial, multiple enteric organisms with an intra-abdominal source
Relapse = same organism within 4 weeks of completing therapy; recurrence = different organism within 4 weeks; repeat = same organism after 4 weeks
Peritonitis is the leading cause of technique failure and transfer to haemodialysis, and carries substantial mortality
- ISPD targets: <=0.40 episodes per patient-year, >80% of patients peritonitis-free per year
Prevention: exit-site mupirocin or gentamicin cream, staff retraining after each episode, antibiotic prophylaxis before colonoscopy and dental or gynaecological procedures, treat constipation
In an unwell PD patient, always look at the bag - a cloudy effluent is the diagnosis, and the sample must be taken before antibiotics

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