Microbiology of Respiratory Tract Infection 2

Question 1

describe the 3 main routes of transmission

Answer 1

contact (touch)

airborne;
small particles
travels long distances
limited indications - multi-drug resistant TB, some viruses, respiratory tract infection undergoing aerosol generating procedures
precautions - standard infection control and filtering face place

droplet;
large molecules
spread via direct contact of droplets with mucous membranes (droplet, surface, contact spread)
precautions - patient in a single room

Question 2

describe defences of the upper respiratory tract

Answer 2

host defences;
nasopharynx - nasal hairs, ciliated epithelia, IgA
oropharynx - saliva, sloughing, cough

Question 3

describe colonisers of upper respiratroy tract

Answer 3

gram postive;
alpha-haemolytic streptococci - strep pneumoniae
beta-haemolytic streptococci - strep pyogenes
staphylococcus aureus

gram negative;
haemophilus influenzae (blood loving species)
moraxella catarrhalis

Question 4

describe conducting airways defences

Answer 4

includes the trachea and bronchi;
mucociliary escalator 
cough
AMPs
cellular and humoral immunity 
infections can occur when there are changes;
trauma/intubation of airway
abnormalities of defence 
e.g. ciliary escalator and others as occurs COPD, changes during CF
virulent pathogen/large inoculum

Question 5

describe CF

Answer 5

inefficient clearance and build-up of mucus
repeated chest infections and chronic colonisation;
staph aureus, haemophilus influenzae, strep pneumoniae, pseudomonas aeruginosa, burkholderia cepacia (plus more)

Question 6

describe acute bronchitis

Answer 6

90%
preceded by upper respiratory tract infection (‘the cold in the chest’)
no antibiotics

Question 7

describe COPD

Answer 7

30% viral
50% bacterial
20%?
haemophilus influenzae and moraxella catarrhalis, streptococcus pneumoniae, gram negatives (plus more)

Question 8

describe defences of lower respiratory tract

Answer 8

lung defences;
normally relatively sterile
no ciliary escalator
alveolar lining fluid - surfactant, Ig, complement, FFA, AMP
alveolar macrophages and neutrophils (phagocytosis causing an inflammatory response)

Question 9

describe community acquired pneumonia

Answer 9

organism reaches the lung
systemic response - immune activation and infiltration
fluid and cellular build up in alveoli leading to impaired gas exchange

microbiology;
streptococcus pneumoniae - most common, 70%
atypicals/viruses - 20%
haemophilus influenzae - 5%
staphylococcus aureus - 4%
other bacteria - 1%

diagnosed via sputum culture and viral PCR

Question 10

describe infections that can be caused by streptococcus pneumoniae

Answer 10

noninvasive pneumococcal disease;
ear infection
sinus infection 
upper respiratory tract infection 
pneumonia without spread to bloodstream

invasive pneumococcal disease;
meningitis
pneumonia with spread to bloodstream
bloodstream infection

Question 11

describe structure and virulence of streptococcus pneumoniae

Answer 11

capsule;
key virulence factor
anti-phagocytic
for sero-typing 
basis for vaccination 
rough strains (avirulent)

surface adhesions
pneumolysin (cytotoxin)
sIgA protease
teichoic acid
H2O2

Question 12

describe types of pneumonia

Answer 12

typical - streptococcus pneumoniae
atypical - mycoplasma pneumoniae, legionella pneumonia, chlamoydophila pneumonia, chlamydia psitacci, viruses
hospital acquired (including ventilator associated)
aspiration
immunosuppressed/special population - pneumocystis jiroveci, aspergillus sp., endemic mycoses, TB

Question 13

describe legionella pneumonia

Answer 13

atypical
gram negative (unusual cell wall structure)
obligate intracellular organism - resides with water amoeba (provides nutrients and protection)
pathogenesis - invades alveolar macrophages and replicates

transmitted via inhalation of contaminated water droplet (risk factor - contaminated aerosolised water)

Question 14

describe walking pneumonia

Answer 14

non productive cough
rash
organism has no cell wall - no amoxicillin

Question 15

describe staphylcoccus pneumonia

Answer 15

post influenza

haematogenous spread of staphylococcus aureus (cardiovascular infection)

Question 16

describe relative bradycardia

Answer 16

10 beats per degree rise in temperture 
seen in;
legionella 
mycoplasma 
tularaemia 
chlamydia

Question 17

describe hospital acquired pneumonia

Answer 17

60% gram negative - E Coli, klebsiella spp, pseudomonas spp

CAP organisms - S aureus, anaerobes

Question 18

describe pulmonary infiltrates with eosinophilia

Answer 18

non infective causes
parasites - ascaris, schisto, dirofilaria
brucella
endemic mycoses
psittacosis
TB

Question 19

describe whooping cough (pertussis)

Answer 19

acute trachea bronchitis 
cold like symptoms 
paroxysmal coughing (2 weeks)
repeated violent exhalations with severe inspiratory whoop, vomiting common
residual cough for month or more 

microbiology;
bordetella pertussis
gram negative coccobacillus
exclusive human pathogen
vaccine preventable

symptoms start 3 days post exposure to bacteria