Community-acquired Pneumonia (CAP)

Question 1

What is CAP?

Answer 1

CAP is defined as pneumonia acquired outside hospital facilities.
Community-acquired pneumonia infers that the infection has been acquired without any contact with healthcare services.
It is common and has an incidence of ~1 in 100 people per year of which 20-40% will require hospital admission.

Question 2

How does pneumonia typically present?

Answer 2

Typically characterised by a new lung infiltrate on chest x-ray, together with one or more of the following: fever, chills, cough, sputum production, dyspnoea, myalgia, arthralgia, pleuritic pain.

Question 3

What should do with patients with suspected CAP?

Answer 3

Order a chest x-ray.

Order sputum and blood cultures for patients with severe CAP.

Question 4

Typical causes of pneumonia

Answer 4

Streptococcus pneumoniae
Haemophilus influenzae
Klebsiella pneumoniae
Staphylococcus aureus

Question 5

Atypical causes of pneumonia

Answer 5

Mycoplasma pneumoniae
Legionella pneumophilia aka Legionnaire’s disease
Chlamydia pneumoniae
Chlamydia psittaci

Question 6

What is streptococcus pneumoniae?

Answer 6

Gram-positive coccus.
The commonest cause of CAP, up to 80% of infections
Can be detected from blood culture (in 30% of cases) or via urinary antigen
The vaccine is available for babies and > 65-year-olds, for immunosuppressed and asplenic patients and those with long term conditions. Rates of infection have fallen due to immunisation

Question 7

What is haemophilus influenzae?

Answer 7

Gram-negative bacillus
Rates of infection have fallen as children now immunised. Note: vaccine does not cover for all serotypes and is not particularly efficient in adults
Around 20% of UK strains now resistant to penicillins

Question 8

What is Klebsiella pneumoniae?

Answer 8

Gram-negative bacillus
The commensal organism of the GI tract
Elderly patients and people with comorbidities at increased risk, alcohol excess also risk factor
Clinically tends to affect upper lobes
Inherently resistant to penicillins, cephalosporins recommended, penicillin combined with a beta-lactamase inhibitor may be an option.

Question 9

What is staphylococcus aureus?

Answer 9

Gram-positive coccus
A rare cause of CAP (2% of cases), more common after influenza or as septic emboli.
IVDU at risk
Chronic lung pathology also a risk factor ie cystic fibrosis and bronchiectasis
Flucloxacillin mainstay of therapy but important to consider MRSA if not improving

Question 10

What is Mycoplasma pneumoniae?

Answer 10

Can be associated with epidemics
Tend to affect younger patients
Dry cough 
Patchy consolidation on CXR
Cannot be cultured in routine laboratories, diagnosis by PCR or serology
Treat with macrolides

Question 11

What is legionella pneumophilia aka Legionnaire’s disease?

Answer 11

Occasionally sporadic cases but often occur in outbreaks, associated with air conditioning systems. Think of this in patients who have recently been on holiday
Tends to affect males (2:1 ratio) and smokers
Prodromal syndrome of high fevers before a dry cough develops
Can be diagnosed with urinary antigen testing
Treat with macrolides

Question 12

What is Chlamydia pneumoniae?

Answer 12

5-10% of CAP
Occurs in outbreaks in families and institutions
Young adults and extremes of age vulnerable
Diagnosis made on acute and convalescent serology or PCR
Treat with macrolide or doxycycline

Question 13

What is Chlamydia psittaci?

Answer 13

Around 3% of CAP
Classically associated with contact with birds esp. parrots and pigeons
Can occasionally cause hepatosplenomegaly
Diagnosis made on acute and convalescent serology or PCR
Treat with macrolide or doxycycline

Question 14

Classification of pneumonia

Answer 14

Pneumonia is classically divided into typical and atypical organisms based on historical laboratory techniques: typical organisms can be cultured in the laboratory whereas atypical organisms are intracellular pathogens and cannot be cultured using standard methods and alternative diagnostic tools are needed.
This division is clinically relevant as atypical organisms need to be treated with antibiotics which get into intracellular space (e.g. macrolides).
Also, atypical organisms do not possess a cell wall on which penicillins or cephalosporins can act.

Question 15

Pathophysiology of pneumonia

Answer 15

Pneumonia develops subsequent to the invasion and overgrowth of a pathogenic microorganism in the lung parenchyma, which overwhelms host defences and produces intra-alveolar exudates.
Impaired immune response or dysfunction of defence mechanism can increase the risk of respiratory infections.

Question 16

What can cause impaired immune response?

Answer 16

HIV infection

Advanced age

Question 17

What can cause the dysfunction of defence mechanism?

Answer 17

Current or passive smoking
COPD
Aspiration

Question 18

How can pathogens reach the lower respiratory tract?

Answer 18

Through 4 mechanisms:
Inhalation
Aspiration of oropharyngeal secretions into the trachea, the primary route through which pathogens enter the lower airways.
Haematogenous spread from a localised infected site (i.e right-sided endocarditis)
Direct extension from adjacent infected foci (e.g. TB can spread contiguously from the lymph nodes to the pericardium or the lung)

Question 19

Signs & symptoms of pneumonia

Answer 19

Cough with increasing sputum production 
Fever or chills 
Dyspnoea 
Pleuritic pain 
Abnormal auscultatory findings. 
Myalgia 
Arthralgia 
Dullness to percussion 
Confusion

Question 20

Risk factors of pneumonia

Answer 20

Age >65 
Residence in a healthcare setting. 
COPD 
Exposure to cigarette smoke
Alcohol abuse
Poor oral hygiene 
Use of acid-reducing drugs, inhaled corticosteroids, antipsychotics, antidiabetic drugs. 
Contact with children 
HIV infection

Question 21

Investigations of pneumonia

Answer 21

Chest x-ray - new infiltrate provides a definitive diagnosis of pneumonia.
FBC- elevated white cell count
Serum electrolytes, urea- normal
LFTs- normal
Blood culture- the growth of causative bacterial species
Sputum culture- Causative bacterial species
ABGs
Blood glucose
Lung ultrasound
CT ultrasound
Urinary antigen testing for legionella and pneumococcus
Serum procalcitonin- may be elevated (a sensitive marker of progress in pneumonia)
PCR- viral causes

Question 22

Differentials of CAP

Answer 22

Acute bronchitis 
Congestive heart failure 
COPD exacerbation 
Asthma exacerbation 
Bronchiectasis exacerbation 
TB 
Lung cancer or lung mets. 
Empyema- Empyema is defined as a collection of pus in the pleural cavity, gram-positive, or culture from the pleural fluid.

Question 23

What is CURB-65?

Answer 23

Curb-65 stratifies patients on the basis of the presence of confusion, urea levels >7 mmol/L, RR >30, BP <90/60 mmHg, and age > 65 years.
In pneumonia, patients with a validated clinical prediction rule for prognosis, along with clinical judgement to determine whether the patient should be treated as an inpatient or outpatient.

Question 24

Scoring for CURB-65

Answer 24

Confusion-1
Urea- 1
RR-1
BP- 1
Age >65- 1
Score:
0-1- Low risk- recommendation is for outpatient care: mortality <3
2- Moderate risk- Hospitalisation. Mortality 9%
3-5: High risk- ICU (30 day mortality 15-40%)

Question 25

Why is CURB-65 not always helpful?

Answer 25

Patients under age 65 can't score as highly as older patients. Patients with chronic renal impairment with normal urea of around 7 may score an extra point but it may be their baseline. It is important to review the current renal function in comparison to older results.

Question 26

Management of CAP?

Answer 26

Determine whether the patient should be treated as an inpatient. PSI is more specific than CURB-65 for this. Healthy patients w/o comorbidities: Amoxicillin Doxycycline Macrolide (azithromycin or clarithromycin) Only use a macrolide in areas with pneumococcal resistance to macrolides <25% and when there is CI to alternative therapies. Patients with co-morbidities (chronic heart, lung, liver or renal disease, DM, alcohol abuse, malignancy): Combination therapy with amoxicillin/clavulanate or a cephalosporin (e.g. cefpodoxime, cefuroxime) plus a macrolide or doxycycline. Monotherapy with a respiratory fluoroquinolone (e.g. levofloxacin, moxifloxacin, gemifloxacin)

Question 27

Treatment of CAP in inpatients

Answer 27

Hypotension- vasopressor therapy Oxygen therapy as necessary >92% IV fluids if needed Monitor Obs Monitor CRP Non-severe CAP: Beta-lactam plus a macrolide Monotherapy with a respiratory fluoroquinolone (e.g. levofloxacin) Combination therapy with beta-lactam plus doxycycline in patients who have CI to both macrolide and fluoroquinolones. Start empirical antibiotic treatment ASAP: Treat for a minimum of 5 days. Switch antibiotics to organism-specific antimicrobial therapy when the causative organism is revealed. Add anti-viral treatment (e.g oseltamivir) to antimicrobial treatment in patients with CAP who test positive for influenza in the inpatient setting.

Question 28

What is the natural history of inflammation in pneumonia?

Answer 28

In the vast majority of patients, as the infection comes under control, the inflammation resolves, usually completely and the lung regains its usual architecture. In a small group of patients, the inflammatory process does not resolve completely and in such patients organisation, abscess formation or fibrosis may result in chronic signs and symptoms.

Question 29

Complications of CAP

Answer 29

``` Septic shock- prevalence in a very old patient (>80 years) with CAP was 71%. Acute respiratory distress syndrome (ARDS) Antibiotic-associated c.dif colitis Heart failure ACS Cardiac arrhythmias Necrotising pneumonia- rare Lung abscess- rare Pleural effusion- very common ```

Question 30

Pleural effusion in pneumonia

Answer 30

Pleural effusion is common in pneumonia and complicates around 50% of cases. The majority are simple exudates however some can become empyema. Empyema is a collection of pus in the pleural space, signs of this can be swinging fevers and continued high inflammatory markers in the presence of appropriate antimicrobials. It is essential to sample this fluid and if empyema diagnosed, the fluid drained as antimicrobial penetration into pus is poor. Lung abscess is a rare complication of pneumonia and refers to localised pus within the lung tissue with cavity formation. This can be seen on X-ray or CT.

Question 31

Pneumonia in kids

Answer 31

Neonates are at risk for pneumonia caused by E-coli, group B streptococcus and Listeria monocytogenes. Between 1-6 months by chlamydia trachomatis, S.aureus and RSV. From 6 months to 5 years, the most common causes are RSV and para-influenza virus.

Question 32

Causes of viral pneumonia

Answer 32

The commonest viruses to cause pneumonia in adults are influenza A and B. However, adenovirus, para-influenza and the respiratory syncytial virus can also cause pneumonia.

Question 33

Risk factors of viral pneumonia

Answer 33

Patients at extremes of age. Immunosuppressive patients including pregnancy. Coinfection with a viral and bacterial pathogen is associated with greater morbidity and mortality.

Question 34

Diagnoses of viral pneumonia

Answer 34

Diagnosis of these viruses can be made using PCR based techniques: taking a viral throat swab for influenza or respiratory viruses is recommended and is a quick and effective test.

Question 35

Causes of fungal pneumonia

Answer 35

In the UK, pneumocystis jiroveci is the most common cause. Pneumonia is also a key symptom for so-called endemic mycoses (e.g. histoplasmosis, blastomycosis, coccidioidomycosis) that are limited to specific geographic areas (Americas primarily) and seen in fully immunocompetent patients.

Question 36

Risk factors of fungal pneumonia

Answer 36

It is mainly seen in patients with altered cell-mediated immunity (immunodeficiency incl. HIV, immunosuppression e.g. after transplantation) but can also occur in patients with a severe underlying respiratory condition (COPD, CF).