Upper Respiratory Tract Infections Flashcards
Infectious disease accounts for ___ of DALYs according to the WHO, of which the greatest majority is which type of infection?
1/3rd; respiratory tract
Which areas of the respiratory tract contain microbiota?
mouth, nasopharnyx, larynx
Which areas of the respiratory tract normally do not have microbiota?
- paranasal sinuses
- middle ear
- larynx below the epiglottis
- trachea
- bronchi
- bronchioles
- alveoli
- lung tissue
The upper respiratory microbiota contains mainly which type of organisms?
anaerobic, mostly strict; generally harmless
Which are the most common upper respiratory microorganisms of healthy people (>50%)?
- viridans streptococci (alpha-haemolytic) in 100%
- Neisseria species (generally non/low-pathogenic)
- Corynebacterium (C. diptheriae, C. hominis, non-toxicogenic C. diptheriae)
- Gram negative anaerobes
- Haemophilis influenzae (not type B) A, C, D, E, F, non-typable (non-encapsulated)
- Candida albicans (yeast)
- Streptococcus pneumonia (15-85%)
viridans streptococci
- commensals (alpha) in 100% of people
- group of species
- either alpha or non-haemolytic
- can cause dental decay by forming plaque of acid-producing bioforms that can erode enamel
- most important causative organism of infective endocarditis
streptococcus bacteria are
- gram positive cocci (spheres)
- grow in chains or pairs
staphylococcus bacteria are
- gram postive cocci (spheres)
- grape-like clusters
neisseria spp
- gram negative diplococci (coffee beans)
- low-grade/non-pathogenic present in normal URT microbiota
- high-grade pathogenic forms are N. gonorrhoeae (gonococcus) and N. meningitidis (meningococcus)
Corynebacterium spp
- gram positive rods
- include:
- C. diptheriae - non-toxicogenic form is a commensal in URT
- C. hominis (cardiobacterium?) also in URT
Haemophilis influenzae
- gram negative coccobacillary (intermediate shape, short rods)
- facultative anaerobes
- all but type B are common URT commensals in <50% of people
- A, C, D, E, F, non-typable (either non-encapsulated or non-typable encapsulated); B eradicated w/vaccine in children
- can cause low grade or serious infections
Candida albicans
- diploid fungus that grows as yeast
- opportunistic pathogen of URT
- common commensal in >50% normal people
Streptococcus pneumoniae
- most important respiratory, and human pathogen
- gram positive cocci
- alpha-ahemolytic, aerotolerant, aerobic
- commensal of the nasopharynx of >50% healthy people
- found in 15-85% of people dependent on population
- usually higher number serotypes (typically less pathogenic)
- causes:
- major cause of pneumonia
- main cause of community acquired pneumonia (and meningitis) in children and the elderly
- septicemia in HIV pt
- bronchitis
- acute sinusitis
- otitis media
- conjunctivitis
- meningitis
- most common cause of bacterial meningitis in adults and young adults along with N. meningitidis
- bactermia
- sepsis
- osteomyelitis
- septic arthritis
- endocarditis
- peritonitis
- pericarditis
- cellulitis
- brain abcess
- major cause of pneumonia
What are the occasional URT microbiota in healthy people (~1-10%)?
- streptococcus pyogenes
- Group A beta-haemolytic strep
- N. meningitides (meningococci)
- ~1% of people
- may be unencapsulated or less virulent serotypes that do not cause meningitis
- in outbreak, get high carraige rates (>90%) in close communities, but cases in only ~5% (not known why some are immune)
Streptococcus pyogenes
- gram positive cocci
- causative agent of Group A strep infections
- beta haemolytic
- infrequent, commonly pathogenic commensal of skin and URT (~1-10%)
- causes:
- pharyngitis (strep throat)
- impetigo
- TSS
- rheumatic fever auto-immune infection of valves, joints
- postinfectious glomerulonephritis
- sensitive to:
- penicillin
- resistant to:
- certain strains: macrolides, tetracylcines, clindamycin
Neisseria meningitidis/meningococcus
- gram negative diplococcus
- causes meningitis
- except unencapsulated forms
- unencapsulated and less virulent serotypres are found in ~1% of normal healthy URT microbiota
- can have high carraige rates in outbreak (close community) but few incident cases
What are the uncommon URT microbiota in healthy people (<1%)?
- enterobacteria e.g. E. coli
- Pseudomonas
- C. diptheriae
Escherichia coli
- gram negative rods
- facultative anaerobes
- common in lower intestine commensals
- uncommon in URT of healthy persons (<1%)
Pseudomonas
- gram negative aerobic bacteria
- uncommonly found in URT of healthy people (<1%)
Enterobacteria
- gram negative bacteria
- includes:
- Salmonella
- E. coli
- Yerisinia pestis
- Klebsiella
- Shigella
What microorganisms are common in the lungs of healthy persons even though the lungs are considered sterile?
- present in latent state
- cause bad infections in immunocompromised people
- Pneumocystis jirovecii (carinii)
- Mycobacterium tuberculosis
- mediastinal lymph nodes
- CMV, HSV, EBV can remain post-infection in lymph nodes and sensory nerves
Rhinovirus typically causes
- URT infections
- e.g. rhinitis, sinusitis, cold, pharyngitis
Parainfluenza viruses, H. influenzae, and influenza virus typically cause
- both URT and LRT infections
Pertussis typically causes
- LRTI
RSV typically causes
- URT, predominantly LRT
- causes very few infections in between
What are the frequent aetiological agents that cause the common cold?
- rhinovirus
- parainfluenza virus
- RSV
- enterovirus or corona virus - more common in adults, summer
What are the frequent aetiological agents that cause pharyngitis/tonsilitis?
- with nasal involvement, exclusively caused by viruses:
- adenovirus
- enterovirus
- parainfluenza virus
- influenza virus
- **does not rule out Group A strep as a secondary infective agent
- without nasal involvement:
- viral (as above) + reovirus
- 1/5 cases in children are bacterial:
- Group A strep, Group C and Group G
- strep pyogenes
- can spread, causing cellulitis (face), septicaemia, post-infective complications in rheumatic fever or glomerular nephritis
What are the frequent aetiological agents that cause sinusitis?
- primary: viral (part of common cold syndrome)
- secondary: H. influenzae, Strept. pneumoniae (less virulent types)
- opportunistic URT commensals, take advantage of viral infection
What are the frequent aetiological agents that cause otitis media?
- pneumocicci
- H. influenzae
- M. catarrhalis (URT commensal)
What are the frequent aetiological agents that cause epiglottitis?
- H. influenzae type B
- more or less eradicated by vaccine
What are the frequent aetiological agents that cause Croup (LTB)?
- viral
- parainfluenza, influenza A, RSV
What is the pathogenesis of the common cold?
*also applies to many viraul URTI*
- virus is absorbed into the nasal epithelium (sits on BM and lamina propria)
- replicates and damages the cells - clear fluid produced from LP (runny nose, sore throat)
- inflammatory response follows (highly infective)
- phagocytes enter to deal with damaged tisse
- commensals take advantage of damaged epithelium
- replicate even in presence of phagocytes
- more phagocytes enter, fluid becomes purulent (yellow/green) with inflammatory cells
- IFN and Ab production clear infection and epithelial damage resolves
- Follicular tonsilitis
- could be strep (pus), need to assess fever, rash, neck lymph nodes
- can take a throat swab
- clinical evidence gives little guidance to causative agent
- Infectious mononucleosis
- present with low grade fever, generally unwell, tired, lethargic
- can diagnose on FBC (specific serology for EBV - this is the most common infection of EBV)
- diptheria
- rare in areas with vaccine
- inflammation in throat, palate
- herpangina
- caused by coxsackie A (enterovirus)
- enteroviruses are ssRNA, unenveloped, and live in RT and GIT where they replicate
- hand foot and mouth disease
- mainly caused by coxsackie virus, or enterovirus 71
