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Atypical infections

Section: Critical care

Curriculum: Curriculum, page 48

Human immunodeficiency virus

General

  • Single stranded RNA virus
  • Infects CD4 T lymphocytes primarily
  • Transmission - sexual, blood, vertical
  • CD4 T lymphocyte count = <200 or at any level with an AIDS defining condition or opportunistic infection (e,g, pneumocystis jirovicii) = AIDS
  • AIDS defining cancers

Pathophysiology

  • Single stranded RNA virus
  • Mechanism
    • Viral entry into CD4+ T cells
    • HIV release its RNA Genome into the cytoplasm as well as viral enzyme reverse transcriptase
    • Replication generating a DNA copy (reverse transcriptase)
    • Incorporating into host DNA via integrase
    • The host cell machinery transcribes the proviral DNA into RNA and the virus is assembled and then buds off the host cell acquiring an envelope from the host membrane
  • Co receptors needed for binding
  • Primarily affect CD4 T lymphocytes
    • Cell death - apoptosis
    • Cell destruction - architectures and cellular composition of lymphoid tissue
  • Also affects macrophages, monocytes and dendritic cells

Clinical

  • Acute - viral type illness e.g. fever, sore throat, LN, aches, resolves within 2-4 wks
  • Chronic - ongoing viral replication in lymphoid tissue
  • Clinical features
  • Opportunistic infections
    • Pneumocystis carinii
    • Candida incl thrush
    • CMV - retinitis
    • Mycobacterial - TB
    • Cryptococcus neoformans  - diarrhoea, meningitis
    • Toxoplasma gondii
    • Crypto
    • HSV
    • Salmonella
  • AIDS neoplasia

Progression to AIDS

  1. Acute infection: High viral load, transient symptoms, and initial CD4+ T cell depletion.
  2. Clinical latency: Slow, ongoing loss of CD4+ T cells with minimal symptoms.
  3. AIDS: Severe immunosuppression, characterized by opportunistic infections, malignancies, and CD4+ T cell counts below 200 cells/μL.

Tracked by

  • CD4 count - expressed as percentage of lymphocytes

Bloods

  • ELISA = enzyme linked immunosorbent assay - detect HIV AB
  • PCR test to confirm
  • Monitor
    • CD4 count - <200 = AIDS, monitor antiretroviral therapy response
    • HIV viral load
    • CD4:CD8 ratio - lower = increased frailty and mortality

Universal precautions

  • Universal precautions are a set of infection control practices designed to prevent the transmission of bloodborne pathogens (e.g., HIV, hepatitis B, and hepatitis C) and other infectious agents through exposure to blood, bodily fluids, and other potentially infectious materials (OPIM)

Operative precautions

  • Normal pre op screening
  • Have higher rates of morbidity and mortality
    • Marginally
    • Worse for AIDS pts
    • Review meds preop
    • If oral absorption concerning for antiretrovirals that are needed - give IV option
    • Most post op infection in HIV pt is usual ones
      • But if low CD4 count have high suspicion for opportunistic infection
    • Low risk of transmission to healthcare workers

Other surgical implications

  • Lower threshold for defunctioning
  • Higher incidence of wound complications
  • Higher risk of infection for oral and anal surgery

Tuberculosis

  • Caused by Mycobacterium tuberculosis, a slow-growing, acid-fast bacillus (AFB)
  • Transmission
    • Airborne droplets expelled when an infected person coughs, sneezes, or speaks.
  • Microbiology
    • Mycobacterium tuberculosis
    • Aerobic
    • Acid fast bacilli
  • Acquired pulmonary infection
  • Can disseminate to any organ system

Presentation in General Surgery

  • Lymphadenopathy
  • GI - peritonitis, ileal, colitis perianal sepsis, fissure, fistula
  • Abdo - retroperitoneal mass - renal, adrenal, splenic, liver
  • Psoas abscess
  • Breast - granulomatous mastitis

Pathology

  • Primary
    • Mycobacteria inhaled
    • Alveolar macrophages phagocytose the bacteria but cannot always kill them due to the bacteria’s ability to inhibit phagosome-lysosome fusion.
    • The bacteria replicate intracellularly, triggering an immune response.
    • T lymphocytes and macrophages form granulomas to contain the infection, leading to the characteristic caseating necrosis.
  • Stages of TB:
    • Latent TB: The immune system contains the bacteria, and the infection remains asymptomatic and non-contagious.
    • Active TB: Reactivation or progression of the disease occurs when the immune system cannot contain the infection, leading to symptoms.
  • Extrapulmonary TB:
    • Bacteria can spread hematogenously, causing TB in other organs like lymph nodes, bones (Pott’s disease), CNS (meningitis), or genitourinary system.

Investigations

  • Gram stain - Acid Fast bacillus
  • Microbial culture takes 6 weeks
  • Mantoux
  • Interferon-Gamma Release Assays (IGRAs): Blood tests (e.g., QuantiFERON-TB Gold)
  • CXR

Management

  • Rifampicin for 4 months - others are isoniazid, pyrazinamide and ethambutol
  • Prevention - BCG vaccination

Actinomycosis

Organism

  • Caused by Actinomyces israelii (most commonly)
  • Gram-positive, filamentous, non–acid-fast anaerobic bacteria
  • Commensal in the oral cavity, gastrointestinal tract, and female genital tract
  • Becomes pathogenic when mucosal barriers are breached (e.g. surgery, trauma, perforation)

Pathophysiology

  • Requires devitalised or hypoxic tissue and anaerobic conditions to establish infection
  • Leads to chronic, indolent infection characterised by:
    • Granulomatous inflammation
    • Dense fibrosis and induration
    • Multiple abscesses and sinus tract formation
  • Produces characteristic “sulphur granules”
    • Yellowish microcolonies of organisms seen in pus or tissue

Common surgical sites and mimics

  • Cervicofacial (50–60%)
    • “Lumpy jaw” — often post-dental procedures or trauma
  • Thoracic
    • Pulmonary or chest wall masses, may mimic malignancy or TB
  • Abdominal and pelvic (15–20%)
    • Mimics malignancy, Crohn’s disease, diverticulitis, tubo-ovarian abscess
    • Often follows perforated appendicitis, bowel surgery, or IUD use

Clinical features

  • Chronic indurated mass with multiple discharging sinuses
  • Minimal systemic toxicity despite extensive disease
  • May cross tissue planes and anatomical boundaries
  • Intraoperatively may appear as dense fibrotic mass with abscesses or sinuses

Diagnosis

  • Clinical suspicion important due to non-specific imaging and slow growth
  • Imaging may show mass-like lesion, abscesses, fistulae, or sinus tracts
  • Sulphur granules in pus (seen on microscopy)
  • Culture of aspirates/tissue (requires prolonged anaerobic incubation)
  • Histopathology: filamentous bacteria in granules within inflammatory tissue

Treatment

  • High-dose penicillin or amoxicillin for prolonged duration (6–12 months)
    • Alternatives: doxycycline, clindamycin if penicillin-allergic
  • Surgical drainage or debridement may be required
    • Especially for large abscesses, sinuses, or to exclude malignancy
  • IUD removal if pelvic actinomycosis suspected

Prognosis

  • Excellent with prolonged antibiotic therapy and surgical control if needed
  • Recurrence possible with incomplete treatment or poor source control

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