Pneumonia is inflammation of the lung alveoli which impairs gaseous enhance as they are filled with blood, mucous, fluid and/or cellular infiltrates.
We can classify it in 2 manners: either by the causative agent or the aetiological mechanism causing the disease. In this CCC we will discuss both classifications.
Pathophysiology
Invasion and growth of a pathogen in the parenchyma of the lung leads to inflammation and infiltration by neutrophils. These neutrophils release cytokines which activate immune response and lead to pyrexia (fever). Fluid and pus accumulation begin to accumulate in the alveoli → impairing gaseous exchange as the diffusion distance is increased and surface area decreased. This ultimately leads to hypoxia, the characteristic of pneumonia.
⚠️ Risk factors
- Age <5 or >65 years old
- Smoking
- Recent RTI
- Chronic respiratory disease
- Immunosuppression
- Aspiration risk (Parkinson’s or neurological diseases, or oesophageal obstruction).
- IV drug users
- Co-morbidities (diabetes, CVD)
- Alcoholism
🔢 Classification
An acute nosocomial LRTI developing at least 48 hours after hospital admission. It can be divided into:
- Early HAP - <5 days of admission. Most commonly caused by strep pneumoniae.
- Late HAP - >5 days of admission. Most commonly caused by:
- S aureus (including MRSA)
- Gram negative bacteria, such as: pseudomonas aeruginosa, haemophilus influenzae
- Intestinal gram negative bacteria, such as: E. coli, actinobacter, klebsiella.
This is simply a pneumonia acquired outside of the hospital. It is similar to any other LRTI:
Common causative agents include:
- ⭐️ Strep pneumoniae
- Haemophilus influenzae
- S aureus and MRSA
- Chlamydia psittaci and chlamydia pneumoniae
- Influenza virus
- Any of the other previously mentioned organisms.
Patients who have an dysphagia (most at risk are stroke, dementia, epilepsy, multiple sclerosis, Parkinson’s disease, motor neurone disease) have unsafe swallowing and can direct food into their bronchial tree. Similarly, patients who have gastric emptying issues or issues with their cough (for example patients under a general anaesthetic) may have oropharyngeal aspirates containing gastric acid as well as aerobic and anaerobic bacteria. The acidity and bacteria may lead to inflammation as well as chemical pneumonitis.
⚠️ Risk factors
- Neurological abnormalities - impaired consciousness, stroke, myasthenia gravis, bulbar palsy (bilateral impairment of CN 9, 10, 11, 12), multiple sclerosis, dementia, Parkinson’s, motor neurone disease).
- Alcoholism
- General anaesthesia and surgery
- Achalasia
- GORD
- Intubation
- Poor dental hygiene and oral infections
- Impaired mucociliary clearance
Aspiration pneumonias most commonly affect the right middle and lower lung due to it being wider and more vertical than the left bronchus (facilitating the passage of aspirates).
🦠 Causative agents
Aerobic
Strep pneumoniae
Staph aureus
Haemophilus influenzae
Pseudomonas aeruginosa
Anaerobic
Klebsiella - this is often seen in aspiration lobar pneumonia in alcoholics
Bacteroides
Prevotella
Fusobacterium
Peptostreptococcus
🦠 Causative agents
Bacterial infections are the most common cause of pneumonia. The most common causative agents include:
- Strep. pneumoniae - 80% of all cases.
- H. influenzae
- Mycoplasma pneumoniae
- S. aureus
Other bacterial species we will discuss include:
- Legionella
- Klebsiella
- Influenza virus - most common cause of viral pneumonia in adults.
- Parainfluenza
- RSV
- SARS-CoV2
Much rarer but can occur with pneumocystis jiroveci especially in HIV positive individuals with a CD4+ count <200cells/uL.
We will now discuss some specific types of pneumonia (based on the causative agents):
Staphylococcal pneumonia is a bilateral cavitating bronchopneumonia (a necrotising pneumonia, the 2 terms are synonymous). It occurs due to an infection from staphylococcus aureus.
It often occurs in Immunocompromised patients as it is an opportunistic bacteria (1/3rd of individuals carry staph aureus in their nasal cavity).
Risk increases with IVDUs, elderly patients or patients with influenza infection.
Another cavitating pneumonia, often in the upper lobes. It presents with a distinct sputum known as red-currant jam sputum (due to its appearance). It occurs with klebsiella pneumoniae infection (a gram negative rod).
⚠️ Risk factors: immunocompromised (elderly, alcoholics, diabetics), malignancy, COPD, long-term steroid use, renal failure.
It can cause complications such as empyema, lung abscesses and pleural adhesions.
An atypical pneumonia - this is a pneumonia caused by atypical organisms that are not detectable on Gram stain and cannot be cultured using standard methods. The most common organisms are mycoplasma pneumoniae, chlamydophila pneumoniae, and legionella pneumophila.
Atypical pneumonias are also referred to as a walking pneumonia, usually because it is milder and does not impair one’s activities. Constitutional symptoms tend to predominate over the respiratory symptoms.
😷 Presentation
It’s onset is more gradual and prolonged.
- Myalgia
- Arthralgia
- Headache
- Dry cough
🚨 Complications
- Erythema multiforme - a type 4 hypersensitivity reaction that has characteristic target lesions.
- Stevens-Johnson syndrome - a disorder of the skin and mucous membranes.
- Meningoencephalitis and Guillan-Barre syndrome
- Bullous myringitis - painful vesicles on the tympanic membrane.
- Pericarditis/myocarditis
- Hepatitis or pancreatitis
- Acute glomerulonephritis
- Autoimmune haemolytic anaemia
There are a set of IgM antibodies that recognise antigens on red blood cells at temperatures below our core temperature. When they become activated that agglutinate RBCs which leads to extravascular haemolysis → anaemia. Secondary cold agglutinin disease (CAD) is a complication of diseases such as infection, autoimmune disorders, lymphoid malignancy or more. Acquisition of these diseases leads to an increase in cold agglutinin antibodies which increases the risk of haemolytic anaemia.
🔍 Investigations
Atypical pneumonias are usually not culture-based diagnosis.
🥇 Mycoplasma serology or PCR
🥇 Cold agglutination test
CXR - bilateral consolidation
🧰 Management
As mycoplasma does not have a cell wall, it is resistant to B-lactam antibiotics.
Tetracyclines or macrolides (erythromycin/clarithromycin) are more appropriate choices.
Previously known as pneumocystis carinii, it is a unicellular eukaryote. It is the most common opportunistic infection with AIDS → pneumocystis jiroveci/carinii pneumonia (PCP).
😷 Presentation
- Dyspneoa
- Dry cough
- Fever
- Very few chest signs
It also causes extra-pulmonary manifestations:
- Hepatosplenomegaly
- Lymphadenopathy
- Choroiditis
🧰 Management
- Co-trimoxazole + adjuvant corticosteroids (if the pO2 <9.3kPa). It has reduced deaths by 1/3rd and respiratory failure by 1/2.
- IV pentamidine - in severe cases.
- All HIV patients with CD4+ <200cells/uL should receive PCP prophylaxis
🔍 Investigations
- CXR - bilateral interstitial pulmonary infiltrates. But it may even be normal.
- 🏆 Bronchoalveolar lavage (BAL) - induces sputum samples which are stained with Grocott’s silver stain and shows a characteristic Mexican hat (sombrero) appearance.
Legionnaire’s disease is causes by legionella pneumophilia. It typically colonises water tanks and often is related with air-conditioning systems. These 2 points are very common in exams and so it is worth remembering. Person-to-person transmission is not seen, however.
It is acquired from infected birds (such as parrots), cattle, horse and sheep.
😷 It results in lethargy, arthralgia, headache, anorexia, dry cough and fever.
🚨 It may also result in hepatitis, splenomegaly, nephritis, infective endocarditis, meningoencephalitis, rash.
😷 Presentation
- Cough with purulent sputum
- Dyspnoea
- Chest pain - mostly pleuritic.
- Fever
- Malaise
- Rigors (sudden feeling of cold and shivering followed by a fever and excessive sweating)
- Systemic infection signs - such as pyrexia, tachycardia, hypotension, confusion and tachypnoea.
🩺 Examination findings
- Low oxygen saturations
- Auscultation may show reduced breath sounds bronchial breathing (harsh and loud sounds on inspiration and expiration), crepitations.
- Dullness on percussion
- Increased vocal resonance
- Pleural rub
💯 Scoring
In the community/primary care setting, pneumonia should be assessed for using the CRB65 criteria:
Criterion | Marker |
C | Confusion - abbreviated mental test score <8/10 |
R | Respiration rate >30/min |
B | Blood pressure <90mmHg (systolic) and/or <60mmHg diastolic. |
65 | >65 years |
Each criterion score 1. Patients are stratified for their risk of death accordingly:
- 0 - mortality risk <1%.
- 1 or 2 - mortality risk 1-10%
- 3 or 4 - mortality risk >10%
In the hospital/secondary care setting, pneumonia should be assessed for using the CURB65 criteria:
Criterion | Marker |
C | Confusion - abbreviated mental test score <8/10 |
U | Urea >7mmol/L |
R | Respiration rate >30/min |
B | Blood pressure <90mmHg (systolic) and/or <60mmHg diastolic. |
65 | >65 years |
Each criterion score 1. Patients are stratified for their risk of death accordingly:
- 0 - 0.7%
- 1 - 3.2%
- 2 - 13%
- 3 - 17%
- 4 - 41.5%
- 5 - 57%
The CURB-65 is used to decide the course of action required for the patient:
- 0-1: Treat as an outpatient
- 2: Consider a short stay in hospital or watch very closely as an outpatient
- 3-5: Requires hospitalization with consideration as to whether they need to be in the intensive care unit
🔍 Investigations
- ABG
- Bloods - FBC (WCC), U&E (for CURB65), LFT, ESR/CRP
- Blood cultures
- Sputum - for MC&S
- NAAT - looking for mycoplasma pneumonia.
- Urine antigen - for legionella and pneumococcal pneumonia.
- Legionella antibodies - in high-risk patients.
- 🏆 CXR - to identify lobar, multi-lobar, cavitation and signs of pleural effusion. Consolidation is typically seen in the area of infection and may also show effusion.
🧰 Management
CURB65 scores help stratify the level of care needed as well:
- 0 or 1 - home-based care
- 2 - hospital based care
- 3+ - intensive care assessment.
Some principles of management are constant, no matter the severity.
- Keep O2 saturations above 94% or 88% in COPD.
- Maintain fluid balance
- Analgesia if they have pleuritic chest pain. Paracetamol is sufficient usually.
Low-severity CAP
- 🥇5 day course of antibiotics
- Amoxicillin
- Erythromycin/clarithromycin or doxycycline if the individual has a penicillin allergy.
Moderate-severity CAP
- 🥇5 day course of dual antibiotic therapy
- Amoxicillin + erythromycin/clarithromycin
- Amoxicillin can be swapped for doxycycline if the individual has a penicillin allergy.
High-severity CAP
- 🥇5 day course of dual antibiotic therapy
- Co-amoxiclav + erythromycin/clarithromycin
- Amoxicillin can be swapped for levofloxacin if the individual has a penicillin allergy.
Erythromycin is preferred in pregnancy.
Antibiotics should be given orally if possible. If given IV they should be reviewed every 48 hours and consider switching to oral if possible.
A repeat CXR should be performed at 6 weeks after resolution to ensure the consolidation has resolved and there is no underlying abnormality.
- Amoxicillin is first-line.
- Clarithromycin/erythromycin should be added if there is no response to first-line therapy or if mycoplasma or chlamydia infection is suspected.
- Co-amoxiclav is recommended if concomitant influenza infection is present.
NICE recommends that patients are not routinely discharged of they have had 2 or more of the following findings in the past 24 hours:
- Temperature >37.5ºC
- RR >24 or more
- HR >100bpm
- SBP <90mmHg
- O2 saturation <90% on room air
- Abnormal mental status
- Inability to eat without assistance
NICE also recommends advising the patient on the following timeframes for resolution of their symptoms:
Time | Progress |
1 week | Fever should have resolved |
1 month | Chest pain and sputum production should have substantially reduced |
1.5 months | Cough and breathlessness should have substantially reduced |
3 months | Most symptoms should have resolved but fatigue may still be present |
6 months | Most people will feel back to normal. |
Add in section on pneumococcal vaccine.