Transmission

Question 0

What is the definition of microbiota/commensals?

Answer 0

Normally harmless/beneficial microbes carried on skin & mucosal surfaces.
Transfer to other sites can be harmful

e.g. Candida albicans (thrush)

Question 1

What is the definition of infection?

Answer 1

Invasion of a host’s tissues by micro-organisms

Question 2

What is vertical transmission? Give an example of a micro-organism transmitted this way.

Answer 2

Transmission of micro-organism between mother and child before or at birth
e.g. HIV, hepatitis

Question 3

What are some of the different types of horizontal transmission? Give an example for each.

Answer 3

Intermediary/vector: third party organism
e.g. Plasmodium falciparum (protozoa causing malaria carried by the female Anopheles mosquito), Flavivirus (virus causing Dengue fever carried by the Aedes aegyphi mosquito)

Direct source to patient: e.g. HIV, hepatitis
Animals to patient: e.g. Rabies virus (Lyssavirus)
Animals to surfaces: e.g. MRSA
Source to environment: e.g. Vibrio cholerae (diarrhoea)
Faecal-oral (water or food): e.g. Salmonella enterica
Droplet: spray (short-reach) e.g. Parvovirus, Bordetella pertussis, Influenza
Aerosol: suspension (long-reach) e.g. Influenza, Mycobacterium tuberculosis

Question 4

What is the definition of a nosocomial infection?

Answer 4

Hospital acquired infection

Question 5

Give some examples of clinically important Gram-positive cocci.

Answer 5

Staphylococcus aureus: osteomyelitis, arthritis, cellulitis, impetigo, pneumonia, endocarditis, septicaemia, lower UTI (+ toxins - toxic shock syndrome, gastroenteritis, scaled skin syndrome)

Coagulase negative staph. (nosocomial infections)

alpha/beta-haemolytic streptococci: toxic shock syndrome, puerperal sepsis, cellulitis, impetigo, pharyngitis

Streptococcus pneumoniae: community aacquired pneumonia, adult bacterial meningitis

Enterococcus faecalis: nosocomial infections

Question 6

Give some examples of clinically important Gram-positive bacilli.

Answer 6

Listeria monocytogenes: immunocompromised, newborn meningitis, listeriosis

Bacillus anthracis: anthrax

Bacillus cereus: spores -> gastroenteritis

Question 7

Give some examples of clinically important Gram-negative cocci.

Answer 7

Neisseria meningitidis: meningitis

Neisseria gonorrhoeae: gonorrhoea

Moraxella catarrhalis: respiratory, middle-ear, eye, CNS, & joint infections

Acinetobacter baumannii: nosocomial infections

Question 8

Give some examples of clinically important Gram-negative bacilli.

Answer 8

Escherichia coli: traveller’s diarrhoea, diarrhoea (infants), UTIs, neonatal meningitis, nosocomial infections

Klebsiella pneumoniae: necrotising lobar pneumonia in alcoholics, diabetics, and those with COPD

Proteus species: gastroenteritis, UTIs

Salmonella typhi: typhoid

Pseudomonas aeruginosa: nosocomial pneumonia, UTIs, surgical site infections, burn infections, immunocompromised

Haemophilus influenzae: otitis media, sinusitis, meningitis, epiglottitis, bronchopneumonia, septic arthritis

Question 9

Give some examples of clinically important fungi.

Answer 9

Yeasts (single-celled): Candida albicans (thrush), Cryptococcus neoformans (AIDS), Pneumocystis jiroveci (pneumonia in AIDS)

Molds (multicellular) =

• Aspergillus species: aspergillosis in AIDS
• Dermatophytes: ringworm, athlete’s foot

Question 10

Give some examples of clinically important parasites.

Answer 10

Protozoa (single-celled):

• Plasmodium falciparum (malaria)
• Cryptosporidium parvum (diarrhoea)
• Trypanosoma cruzi (Chaga’s disease)
• Giardia lamblia (giardiasis)

Helminths (multi-cellular & worms):

• Enterobius vermicularis (roundworm)
• Taenia saginata (tapeworm)
• Schistosoma mansomi (flukes)

Question 11

What are some important factors to consider with an infected patient?

Answer 11

PERSON =

• Age: e.g. 0-3months protected by maternal antibodies, subsequently vulnerable unless vaccinated
• Gender: e.g. males more at risk in general, STIs are generally asymptomatic in men
• Physiological state: e.g. changes in pH of vagina during puberty, commensals in large bowel may cause gestational diabetes in pregnancy
• Pathological state: e.g. when immunosuppressed (AIDS, cancer, chemo) likely to get opportunistic infections
• Social: e.g. lifestyle

TIME = calendar time (time of year e.g. in winter colds, flu, & norovirus incidence increases) & relative time (incubation period & exposure)

PLACE = current & recent (travel history)