6 Respiratory Tract Infections: Bacterial Infections Flashcards
Describe how pneumonia is classified
Pneumonia is classified as:
- Community-acquired (CAP)
- Nosocomial (hospital-acquired)
CAP is further divided into:
- Typical
- Atypical
Describe community-acquired pneumonia (CAP)
- A leading cause of death
- Majority are caused by bacterial pathogens
- Most often due to Streptococcus pneumoniae
Describe how a diagnosis of pneumonia can be made
- The presence of new symptoms or signs of lower respiratory tract infection
AND - New pulmonary shadowing on chest X-ray (sensitivity 50% to 85%)
Give the pathogenesis of Pneumonia
- Microaspiration of oropharyngeal contents during sleep (most common cause)
- Inhalation of aerosol drops ranging in size from 0.5-1 um (2nd most common cause)
- Bloodstream infection (least common cause)
Describe bronchopneumonia
- It begins as acute bronchitis and spreads locally into the lungs
- The lower lobes or right middle lobe are usually involved
- The lung has patchy areas of consolidation
- Microabscesses (pus-filled cystic space) are present in the areas of consolidation
Describe lobar pneumonia
- Complete or almost complete consolidation (air replaces with something else) of a lobe of a lung
List some complications of pneumonia
- Lung abscess, emphysema (pus in the pleural cavity)
- Sepsis
List the causative organisms
- Conventional bacteria cause 60-80% of all cases of CAP
- ‘Atypical’ bacteria cause 10-20% of CAP
- Viruses cause 10-20% of CAP
Describe upper respiratory tract infection
The most common cause is rhinovirus (common cold). Other viruses:
- influenza virus, Adenovirus, enterovirus respiratory syncytial virus
Bacteria may cause roughly 15% of sudden onset pharyngitis presentations.
The most common are:
- Streptococcus pyogenes
How can one make a diagnosis of the common cold
The presence of classical features for rhinovirus infection,
coupled with the absence of signs of a bacterial infection or serious respiratory illness, is sufficient to make the diagnosis of the common cold
The common cold is a clinical diagnosis
(diagnostic testing is not necessary)
Describe how influenza can be tested for:
- Nasal aspirates
- Swabs
best specimens to obtain when testing infants and young children
For adults and older children, swabs + aspirates from the nasopharynx are preferred
Rapid strep swabs can be used to rule out bacterial pharyngitis,
-which could help decrease the number of antibiotics being prescribed for these infections
Give the clinical findings in Lower Respiratory Tract Infection
- High fever with productive cough
- Chest pain
- Tachycardia
- Signs of consolidation (alveolar exudate - higher protein content that transudate)
Describe streptococcus pneumoniae
(gram-positive diplococcus)
- S. pneumoniae is the most common cause of community-acquired pneumonia (CAP)
- The capsular polysaccharide is the major virulence factor (protection against phagocytosis and drying)
- Relative resistance to penicillin
- Rapid onset, productive cough, signs of consolidation
- Urine antigen testing test excellent screen
Describe Haemophilus influenza
Haemophilus influenzae
- gram-negative rod
- Most common bacterial cause of acute exacerbations of COPD
- Most virulent strains have a capsule
H. influenza is a primary cause of CAP in children who have not received Hib (vaccine)
COPD
Describe Pseudomonas aeruginosa
- it is a gram-negative rod
- has a capsule
- green sputum (pyocyanin)
- Water-loving bacteria - often transmitted by ventilators
(hospital-acquired pneumonia - HAP)
(ventilator-acquired pneumonia - VAP)
The most common cause of nosocomial pneumonia and death due to pneumonia in cystic fibrosis
Hospital-acquired pneumonia
Describe Klebsiella penumoniae
- capsule
- common gram -ve organism causing lobar pneumonia in elderly patients in nursing homes
- Common cause of pneumonia in alcoholics
Typical pneumonia associated with blood-tinged, thick, mucoid sputum
- Lobar consolidation and abscess formation is common
Lobar pneumonia
List important bacterial causes of upper respiratory tract infections
Atypical causes:
- Interstitial pneumonia, no signs of consolidation
- Insidious onset, low-grade fever
- Non-productive cough
- Both upper + LRT symptoms
- Flu-like symptoms
Describe mycoplasma pneumoniae
(no cell wall)
- Most common cause of atypical pneumonia (up to 20% of CAP)
- Common in adolescents + military (closed spaces)
- Risk factor for Guillain-Barre syndrome
- Insidious onset - with low-grade fever
Atypical pneumonia
Give some complications of mycoplasma pneumoniae infections (atypical pneumonia)
- Bullous myringitis (painful blisters on the eardrum)
- Cold autoimmune hemolytic anemia - due to anti-IgM (type 2 HSR)
Give the treatment of mycoplasma pneumoniae infections (atypical pneumonia)
- No wall targeting abx
> (resistant to penicillin + cephalosporins)
Give ribosomal abx
e.g. macrolides - erythromycin, azithromycin
Describe legionella pneumophila
It is a gram -ve rod (poorly staining)
- Antigens can also be detected in urine
- Water-loving bacterium (water cooler; mists in the produce of grocery stores, outdoor restaurants in summer, rain forests in zoos)
- More common in alcoholics, smokers, and immunocompromised patients
Atypical pneumonia associated with:
- High fever
- Dry cough
- Flu-like symptoms
Describe nosocomial pneumonia
Pneumonia contracted by a patient in hospital (HAP) - after 48hrs post-admission
- Ventilators (VAP) and intubation
- Opportunistic infection in patients with severe underlying disease
- Antibiotic therapy
- Immunosuppression
List some organisms that can cause nosocomial pneumonia
- Pseudomonas aeruginosa
- E. coli
Gram +ve like S. aureus
Describe the management of pneumonia (CAP)
Most managed in general practice, refer if:
- Symptoms + signs suggest a more serious illness/condition (e.g.
cardiorespiratory failure or sepsis)
OR
- Symptoms are not improving as expected with antibiotics
Other things to consider:
- Bacterial resistance to oral antibiotics
- Consider referring young people with CAP to hospital, or seek specialist paediatric advice on further investigation and management
