MICROBIOLOGY OF LOWER RESPIRATORY TRACT INFECTIONS
LRTI – Any infection of the respiratory tract from the vocal cords downwards.
Flora of LRT
Normal LRT is bacteriologically sterile.
As inhaled particles are trapped by mucus and moved to the upper respiratory tract
by the mucociliary escalator.
Get ABNORMAL FLORA if:
Paralysis of cilia, excessive mucus
Loss of swallowing reflex
Antibiotic therapy WILL affect URT colonization.
Types of LRTI
1. Acute cough (<3w)
2. Bronchiolitis (inflam of bronchioles)
3. Influenza
4. Bronchitis (inflam of mucous membranes of bronchi)
5. Bronchiectasis (abnormal widening of bronchi, increases infection risk)
6. Pneumonia – can be community or hospital acquired.
Chronic Bronchitis – if condition exacerbates then give antibiotic therapy but only if they
have increased breathlessness, sputum volume and sputum purulence. Therefore give
amoxicillin, a tetracycline or a macrolide.
C-REACTIVE PROTEIN
Levels of C protein rise in plasma in response to inflammation.
People presenting with LRTI – consider a C-reactive protein test.
Use this information to determine whether antibiotic therapy is necessary.
If concentration of protein is <20mg/l = don’t offer antibiotic therapy.
If concentration is between 20-100mg/l = consider delayed antibiotic prescription.
If concentration is >100mg/l = offer antibiotic therapy.
CRB65 = Test that scores a patients mortality risk in primary care. Calculated by giving 1
point to each of the following:
Confusion
Raised respiratory rate (>30)
Low BP
Age (>65yrs)
If they score 0 then they don’t require hospitalization, if they score 1 or 2 then a hospital
referral is considered and if >3 then urgent hospitalization.
What are the three commonest pathogens causing CAP in patients?
Mainly Streptococcus pneumonia and Haemophilus influenza then Mycoplasma pneumonia.
LRTI – Any infection of the respiratory tract from the vocal cords downwards.
Flora of LRT
Normal LRT is bacteriologically sterile.
As inhaled particles are trapped by mucus and moved to the upper respiratory tract
by the mucociliary escalator.
Get ABNORMAL FLORA if:
Paralysis of cilia, excessive mucus
Loss of swallowing reflex
Antibiotic therapy WILL affect URT colonization.
Types of LRTI
1. Acute cough (<3w)
2. Bronchiolitis (inflam of bronchioles)
3. Influenza
4. Bronchitis (inflam of mucous membranes of bronchi)
5. Bronchiectasis (abnormal widening of bronchi, increases infection risk)
6. Pneumonia – can be community or hospital acquired.
Chronic Bronchitis – if condition exacerbates then give antibiotic therapy but only if they
have increased breathlessness, sputum volume and sputum purulence. Therefore give
amoxicillin, a tetracycline or a macrolide.
C-REACTIVE PROTEIN
Levels of C protein rise in plasma in response to inflammation.
People presenting with LRTI – consider a C-reactive protein test.
Use this information to determine whether antibiotic therapy is necessary.
If concentration of protein is <20mg/l = don’t offer antibiotic therapy.
If concentration is between 20-100mg/l = consider delayed antibiotic prescription.
If concentration is >100mg/l = offer antibiotic therapy.
CRB65 = Test that scores a patients mortality risk in primary care. Calculated by giving 1
point to each of the following:
Confusion
Raised respiratory rate (>30)
Low BP
Age (>65yrs)
If they score 0 then they don’t require hospitalization, if they score 1 or 2 then a hospital
referral is considered and if >3 then urgent hospitalization.
What are the three commonest pathogens causing CAP in patients?
Mainly Streptococcus pneumonia and Haemophilus influenza then Mycoplasma pneumonia.
