MICRO 25 – Opportunistic Infections
Opportunistic Pathogens
• Organisms of low intrinsic virulence that are not normally
harmful: e.g.
– Coagulase negative staphylococci
– Aspergillus fumigatus
• May cause serious infections in certain circumstances, e.g.
– in an immunocompromised patient
– where a foreign body is present
Immunocompromised Patient
General term
• any patient compromised by virtue of his/her underlying
condition
• e.g. multiple trauma patient in ICU
non-specific
Specific term
• A patient with a recognised deficiency of one or more immune
parameters
• e.g. neutropenic patient on chemotherapy
refers to specific categories of patients
Importance of Opportunistic Infections
• Increased numbers of immunocompromised patients
• Significant cause of morbidity & mortality
• May be polymicrobial & complex
• Bacteria often multi-antibiotic resistant
• Variable clinical presentation – atypical, fever often absent
• May be difficult to diagnose
CAUSES OF IMMUNOCOMPROMISED STATES
Primary – Antibody deficiency syndromes
immunodeficiency – Neutrophil dysfunction e.g. chronic
Rare - Present in early granulomatous disease
infancy or childhood – severe combined immune deficiency (SCID),
complement deficiency states
Secondary – Immunosuppresive therapy: Steroids,
Immunodeficiency chemotherapy
– Malignancy
– Autoimmune disease: Rheumatoid arthritis
– Microbial infection: HIV
– Biochemical abnormalities: Diabetes mellitus,
malnutrition
– Asplenia / hyposplenism
Anatomic lesions Barrier problems – intact skin is a key component
of the body’s defences
o e.g. burns
Inadequate clearance
o e.g. respiratory tract cilia that are abnormal in
structure or function
Obstruction
o e.g. cystic fibrosis, chronic obstructive
pulmonary disease (COPD)
Foreign body
o e.g. a central venous catheter
Name common bacterial, viral, fungal & parasitic causes of opportunistic infections
, Features of Opportunist Pathogens
i. Low pathogenicity & sometimes ubiquitous, e.g. Pneumocystis jirovecii (Pneumocystis carinii), Candida albicans,
S. epidermidis, P. aeruginosa
ii. May be part of normal flora, e.g. S. epidermidis, Candida
iii. Adapt to host & circumstances, e.g. biofilm production
iv. Often difficult to completely eradicate / may relapse, e.g. CMV
v. Variable clinical presentation
vi. Absent normal immune response; negative serology
BACTERIA
Endogenous organisms
• S. epidermidis
• S. aureus
• Gut flora
– E. coli
– Enterococci, including vancomycin-resistant enterococci (VRE)
Exogenous organisms
• S. aureus, including MRSA
• Enterobacteriaecae
• P. aeruginosa
• Listeria
• Atypical mycobacteria & M. tuberculosis
VIRUSES
• Herpes viruses: Latency leading to reactivation
– Herpes simplex virus 1 & 2
– Varicella-zoster virus
– Cytomegalovirus
• Polyomaviruses: Latent in kidney & lymphoid tissue
– JC virus Progressive Multifocal Leukoencephalopathy (PML)
– BK virus (stem cell and renal transplant recipients)
• Parvovirus B19: Can cause profound red cell aplasia
– Persistent infection in immunocompromised / persistent anaemia
• Hepatitis B: chronic carriage or reactivation of latent infection
Fungi
• Candida spp.
– Mucositis, oesophagitis, candidaemia
• Aspergillus fumigatus
– Lower respiratory tract infection
• Cryptococcus neoformans
– Meningitis or meningo-encephalitis
• Pneumocystis jirovecii –PCP
– Pneumonia
Protozoa
Opportunistic Pathogens
• Organisms of low intrinsic virulence that are not normally
harmful: e.g.
– Coagulase negative staphylococci
– Aspergillus fumigatus
• May cause serious infections in certain circumstances, e.g.
– in an immunocompromised patient
– where a foreign body is present
Immunocompromised Patient
General term
• any patient compromised by virtue of his/her underlying
condition
• e.g. multiple trauma patient in ICU
non-specific
Specific term
• A patient with a recognised deficiency of one or more immune
parameters
• e.g. neutropenic patient on chemotherapy
refers to specific categories of patients
Importance of Opportunistic Infections
• Increased numbers of immunocompromised patients
• Significant cause of morbidity & mortality
• May be polymicrobial & complex
• Bacteria often multi-antibiotic resistant
• Variable clinical presentation – atypical, fever often absent
• May be difficult to diagnose
CAUSES OF IMMUNOCOMPROMISED STATES
Primary – Antibody deficiency syndromes
immunodeficiency – Neutrophil dysfunction e.g. chronic
Rare - Present in early granulomatous disease
infancy or childhood – severe combined immune deficiency (SCID),
complement deficiency states
Secondary – Immunosuppresive therapy: Steroids,
Immunodeficiency chemotherapy
– Malignancy
– Autoimmune disease: Rheumatoid arthritis
– Microbial infection: HIV
– Biochemical abnormalities: Diabetes mellitus,
malnutrition
– Asplenia / hyposplenism
Anatomic lesions Barrier problems – intact skin is a key component
of the body’s defences
o e.g. burns
Inadequate clearance
o e.g. respiratory tract cilia that are abnormal in
structure or function
Obstruction
o e.g. cystic fibrosis, chronic obstructive
pulmonary disease (COPD)
Foreign body
o e.g. a central venous catheter
Name common bacterial, viral, fungal & parasitic causes of opportunistic infections
, Features of Opportunist Pathogens
i. Low pathogenicity & sometimes ubiquitous, e.g. Pneumocystis jirovecii (Pneumocystis carinii), Candida albicans,
S. epidermidis, P. aeruginosa
ii. May be part of normal flora, e.g. S. epidermidis, Candida
iii. Adapt to host & circumstances, e.g. biofilm production
iv. Often difficult to completely eradicate / may relapse, e.g. CMV
v. Variable clinical presentation
vi. Absent normal immune response; negative serology
BACTERIA
Endogenous organisms
• S. epidermidis
• S. aureus
• Gut flora
– E. coli
– Enterococci, including vancomycin-resistant enterococci (VRE)
Exogenous organisms
• S. aureus, including MRSA
• Enterobacteriaecae
• P. aeruginosa
• Listeria
• Atypical mycobacteria & M. tuberculosis
VIRUSES
• Herpes viruses: Latency leading to reactivation
– Herpes simplex virus 1 & 2
– Varicella-zoster virus
– Cytomegalovirus
• Polyomaviruses: Latent in kidney & lymphoid tissue
– JC virus Progressive Multifocal Leukoencephalopathy (PML)
– BK virus (stem cell and renal transplant recipients)
• Parvovirus B19: Can cause profound red cell aplasia
– Persistent infection in immunocompromised / persistent anaemia
• Hepatitis B: chronic carriage or reactivation of latent infection
Fungi
• Candida spp.
– Mucositis, oesophagitis, candidaemia
• Aspergillus fumigatus
– Lower respiratory tract infection
• Cryptococcus neoformans
– Meningitis or meningo-encephalitis
• Pneumocystis jirovecii –PCP
– Pneumonia
Protozoa
