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CR - Lower RTIs (ii) - Bacterial Causes of CAP (S pneumoniae…
CR - Lower RTIs (ii) - Bacterial Causes of CAP
S pneumoniae (pneumococcus)
most common (60% of cases)
also causes sinusitis, otitis media, meningitis
abrupt onset
sustained fever
BSI if severe
10-20% mortality
purulent sputum
pleuritic chest pain
parapneumonic effusions in 25%
use Light's criteria to determine transudative vs exudative course
rarely empyema (collection of pus in physiological pleural cavity)
Dx
sputum + blood culture (on blood agar with optochin disk) + sensitivity
urinary antigen
gram +ve coccus in chains
alpha-haemolytic (partial lysis, green)
catalase -ve
optochin sensitive (whereas S viridans is resistant)
Tx
if penicillin susceptible give IV benzylpenicillin + switch to PO amoxicillin if able
IV cefotaxime is penicillin resistant
if MDR give levofloxacin (fluoroquinolone) or vancomycin
prevention = pneumococcal vaccine
covers 13 serotypes
in Irish childhood vaccination programme
also indicated for over 65s + @ risk groups
M Pneumoniae
10-20% of cases
esp in children + young adults
person-person spread by reps droplets
infection only causes pneumonia 10% of time (more common presentations are cough, pharyngitis, rhinorrhoea, ear pain)
extra-pul manifestations
haemolysis (rarely clinically significant)
skin rash (incl SJS)
carditis
encephalitis (esp in children)
Dx
serology
NAAT
NO CELL WALL
Tx
macrolides
tetracyclines
H Influenzae
Dx = sputum culture
fastidious
required CO2, X factor (haemin) or V factor (NAD) or both
chocolate agar (heated blood - RBCs lysed)
gram -ve bacilli/coccobacilli
20% produce B-lactamases
hence resistant to penicillin + amoxicillin
Tx = co-amoxiclav
DOESN'T CAUSE THE FLU
L Pneumophila
infection via inhalation on aerosols from contaminated water
risk factors: smoking, age, immunocompromised
can present as...
Pontiac fever (mild self-limiting systemic symptoms
Legionnaire's disease (severe pneumonia, GI symptoms, ILI, confusion + renal failure if severe)
Dx
Urinary antigen (80%) sensitive
Culture (fastidious, grow on BCYE- buffered charcoal yeast extract)
Tx
macrolides
fluoroquinolones
S aureus
post-influenza + IVDUs @ risk
if strain produces Panton-Valentine leucocidin (PVL) toxin can cause severe necrotising pneumonia in healthy young people (may require ICU)
multifocal pneumonia
abscess formation
C Pneumoniae
person-person spread via resp droplets
intracellular
3-4 wk incubation period
can present as pneumonia, pharyngitis or extra-pul manifestations
Dx
NAAT
serology (detect 1-fold rise in specific IgG titre)
culture
no peptidoglycan in cell wall
Tx
tetracyclines
macrolides
mortality as high as 20% in untxed infection (esp in elderly)
Klebsiella pneumoniae
gram -ve bacillus
alcoholics, elderly, increased aspiration risk, DM @ increased risk
cavitating pneumonia
abscess formation
may require ICU
C Psittaci
intracellular
zoonosis (reservoir = birds)
airborne spread - infection via inhalation of infected secretions/droppings
1-3 wk incubation
presentations
acute ILI (esp fever)
pneumonia
Dx, Tx + mortality in untxed infection same as C pneumoniae
complications rare but severe
Coxiella Burnetii
Q fever
world-wide zoonosis
extreme infectivity (highly infectious @ low doses)
infection via inhalation of aerosols from placenta/partutient fluids of infected lifestolk, or rarely from drinking infected raw milk
humans = incidental hosts
ask about occupation - farmers, vets, abattoir workers
acute infection
ILI
atypical pneumonia
hep
pregnancy complications
tx = doxycycline
assymptomatic in 50% of those infected
1-5% of infected develop chronic infection
esp pregnant, immunocompromised, underlying valvular/vasc disease
usually culture -ve endocarditis
osteomyelitis
vasc graft infections
Tx = combo of doxycycline + rifampicin for a prolonged period
Dx
NAAT (not commonly available)
serology
culture (biosafety level 3 so warn lab if you suspect it)