Mycoplasma Pneumonia (Atypical Pneumonia)
Summary
Mycoplasma pneumoniae is a cell wall-deficient bacterium (smallest free-living organism) causing atypical pneumonia. It is the most common cause of atypical pneumonia in young adults and children. The infection is characterised by an insidious onset, dry cough, and disproportionately mild physical signs compared to chest X-ray findings. It is often called "Walking Pneumonia" because patients remain ambulatory despite radiological consolidation. Crucially, penicillins and cephalosporins are ineffective (no cell wall to target). Treatment requires macrolides (Clarithromycin, Azithromycin) or tetracyclines (Doxycycline). Important extra-pulmonary manifestations include Erythema Multiforme (target lesions), Cold Agglutinin Haemolytic Anaemia, Bullous Myringitis, and neurological complications (Guillain-Barré, Encephalitis). [1,2]
Clinical Pearls
No Cell Wall = No Penicillin: Mycoplasma lacks a cell wall. Beta-lactams (Amoxicillin, Co-amoxiclav) are USELESS. Always use Macrolides or Doxycycline.
"Target Lesions = Mycoplasma": Erythema Multiforme with target lesions in a patient with cough = Mycoplasma until proven otherwise.
"Looks Worse on X-ray Than on Exam": Classic teaching point - patient appears well but CXR shows extensive patchy infiltrates.
Cold Agglutinins: IgM antibodies that agglutinate RBCs at 4°C. Causes Coombs-positive haemolytic anaemia. Tube of blood clumps when placed on ice.
Demographics
| Factor | Notes |
|---|---|
| Age | Peak: 5-20 years (School-aged children, Young adults). |
| Season | All year, but peaks in Autumn/Winter. |
| Setting | Outbreaks in closed communities (Schools, Universities, Military Barracks). |
| Epidemic Cycle | Epidemics occur every 3-7 years. |
Transmission
- Droplet Spread: Close respiratory contact.
- Incubation: 2-3 weeks (Longer than typical pneumonia).
Unique Features of Mycoplasma
- No Cell Wall: Smallest self-replicating bacterium. Cannot be seen on Gram stain. Resistant to beta-lactams.
- P1 Adhesin Protein: Attaches to respiratory epithelium (Ciliated bronchial cells).
- Cytotoxins: Damages respiratory epithelium → Cough, impaired mucociliary clearance.
- Immune-Mediated Damage: Many manifestations (Erythema Multiforme, Haemolysis, Neurological) are autoimmune rather than direct infection.
| Organism | Key Features |
|---|---|
| Mycoplasma pneumoniae | Young adult, Dry cough, Erythema Multiforme, Cold Agglutinins. |
| Chlamydophila pneumoniae | Similar age, Biphasic illness (Pharyngitis → Pneumonia), Hoarseness. |
| Legionella pneumophila | Travel/Water source (Hotels, Spas), Hyponatraemia, Diarrhoea, Confusion, High CRP. |
| Chlamydophila psittaci | Bird contact (Parrot, Pigeon). Headache. |
| Coxiella burnetii (Q Fever) | Farm animal contact (Sheep, Cattle). Hepatitis. |
| Streptococcus pneumoniae (Typical) | Acute onset, Rust-coloured sputum, Dense lobar consolidation, High WCC. |
Pulmonary Features
| Feature | Notes |
|---|---|
| Onset | Insidious (Develops over days-weeks, not hours). |
| Cough | Dry, Hacking, Persistent. Often lasts weeks. |
| Fever | Low-grade (Often less than 38.5°C). |
| Headache, Malaise | Prominent "Flu-like" prodrome. |
| Chest Examination | Often NORMAL or minimal crackles despite extensive CXR changes. |
| "Walking Pneumonia" | Patient appears well enough to "walk into clinic" despite radiological pneumonia. |
Extra-Pulmonary Manifestations (Exam Favourites)
| System | Manifestation | Notes |
|---|---|---|
| Skin | Erythema Multiforme | Target lesions (Iris rash). Classic association. |
| Stevens-Johnson Syndrome | Severe mucosal involvement. Rare but serious. | |
| Haematological | Cold Agglutinin Haemolytic Anaemia | IgM antibodies. Agglutination at cold temperatures. Coombs positive. |
| Ear | Bullous Myringitis | Haemorrhagic blisters on tympanic membrane. Painful. Classic exam buzzword. |
| Neurological | Guillain-Barré Syndrome | Post-infectious demyelination. |
| Encephalitis, Meningitis | Rare. | |
| Cardiac | Myocarditis, Pericarditis | Rare. |
| GI | Diarrhoea, Hepatitis | Less common. |
Blood Tests
| Test | Findings |
|---|---|
| FBC | Often normal. May show mild lymphocytosis. |
| WCC | NOT typically raised (Unlike typical pneumonia). |
| CRP | Mildly elevated (Lower than Legionella). |
| Cold Agglutinins | Positive in 50%. Bedside test: Blood clumps when tube placed on ice. |
| LDH | Elevated if haemolysis. |
Microbiology
| Test | Notes |
|---|---|
| Mycoplasma PCR (Throat Swab / Sputum) | Gold Standard. Rapid, Sensitive. |
| Serology (IgM/IgG) | Traditionally used. IgM appears in first week. 4-fold rise in IgG (Acute vs Convalescent) confirms. Retrospective. |
| Culture | NOT routine. Requires special media (Eaton agar). Slow growth (weeks). |
Imaging
| Imaging | Findings |
|---|---|
| Chest X-Ray | Patchy Reticulonodular Infiltrates (Often bilateral, lower lobes). DISPROPORTIONATE to clinical signs. |
Management Algorithm
SUSPECTED ATYPICAL PNEUMONIA
(Dry cough, Young patient, CXR worse than exam)
↓
CONSIDER MYCOPLASMA
- Check for Extra-pulmonary signs (Rash, Anaemia, Ear)
- Do NOT wait for serology if clinically suspected
↓
ANTIBIOTIC THERAPY
┌──────────────────────────────────────────────────────────┐
│ FIRST LINE: MACROLIDES (Target Protein Synthesis) │
│ - **Clarithromycin 500mg BD** for 5-7 days │
│ - **Azithromycin 500mg OD** for 3-5 days │
│ │
│ ALTERNATIVE (Adults / Macrolide Intolerant): │
│ - **Doxycycline 100mg BD** for 5-7 days │
│ │
│ ALTERNATIVE: Fluoroquinolones (Levofloxacin) │
│ - Reserve for severe cases or resistance │
│ │
│ ❌ DO NOT USE: Amoxicillin, Co-amoxiclav, Penicillin │
│ (No cell wall = No target) │
└──────────────────────────────────────────────────────────┘
↓
COMPLICATIONS MANAGEMENT
- Cold Agglutinin Haemolysis: Keep patient warm. Steroids if severe.
- Erythema Multiforme: Supportive. Steroids controversial.
- Severe Hypoxia: Oxygen. Consider HDU/ICU.
Severity Assessment
- Use CURB-65 Score (as per any CAP) to assess severity:
- Confusion
- Urea >7
- RR ≥30
- BP less than 90 systolic / ≤60 diastolic
- Age ≥65
Duration and Response
- Cough may persist for 2-6 weeks even after successful treatment.
- Improvement usually seen within 48-72 hours of starting appropriate antibiotics.
| Complication | Notes |
|---|---|
| Respiratory Failure | Rare but can occur in elderly or immunocompromised. |
| Haemolytic Anaemia (Cold Agglutinins) | Self-limiting. Avoid cold exposure. Steroids if severe. |
| Neurological (GBS, Encephalitis) | Post-infectious. Immunotherapy may be needed. |
| Stevens-Johnson Syndrome | Mucosal erosions. Ophthalmology review. |
| Persistent Cough | "Post-Mycoplasma Cough" can last weeks post-treatment. |
- Excellent prognosis in immunocompetent individuals.
- Self-limiting in many cases (But antibiotics shorten illness and reduce transmission).
- Mortality: Very low (less than 1%).
- Cough Duration: Can persist for 2-6 weeks even after treatment.
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Community Acquired Pneumonia in Adults | BTS (2015) | Macrolide for atypical cover if no response to beta-lactam. |
| CAP Guidelines | NICE (2023) | Doxycycline or Macrolide for low-severity CAP. |
Landmark Evidence
- No specific Mycoplasma RCTs – treatment recommendations based on mechanism of action (no cell wall) and observational data.
What is Mycoplasma Pneumonia?
It is a type of chest infection caused by a tiny germ called Mycoplasma. Unlike typical chest infections, it builds up slowly and causes a dry, tickly cough that can last for weeks.
Why didn't Amoxicillin work?
Amoxicillin works by attacking the cell wall of bacteria. Mycoplasma doesn't have a cell wall, so Amoxicillin cannot damage it. You need a different antibiotic (Clarithromycin or Doxycycline) that works by a different mechanism.
Why is it called "Walking Pneumonia"?
Because most people feel well enough to keep walking around and going to work/school, even though they technically have pneumonia. The X-ray often looks much worse than the patient feels.
Will my cough ever go away?
Yes, but it can take 2-6 weeks to fully settle, even after the antibiotics have finished. This is normal and doesn't mean the treatment failed.
Primary Sources
- Lim WS, et al. BTS guidelines for the management of community acquired pneumonia in adults. Thorax. 2015;70(Suppl 3):iii1–iii85. PMID: 19734136.
- Waites KB, et al. Mycoplasma pneumoniae and its role as a human pathogen. Clin Microbiol Rev. 2017;30(3):747-809. PMID: 28539503.
Common Exam Questions
- Antibiotic Choice: "Young patient with dry cough, not improving on Amoxicillin. Next antibiotic?"
- Answer: Clarithromycin (or Doxycycline).
- Pathognomonic Sign: "Dry cough + Target lesions on hands?"
- Answer: Mycoplasma (Erythema Multiforme).
- Lack of Cell Wall: "Why are beta-lactams ineffective?"
- Answer: No cell wall – Beta-lactams target cell wall synthesis.
- Haematological Complication: "IgM antibodies causing haemolysis at cold temperatures?"
- Answer: Cold Agglutinins.
Viva Points
- Bullous Myringitis: Classically described in exams. Haemorrhagic blisters on eardrum = Think Mycoplasma.
- Age Group: School-aged children and young adults. Outbreaks in closed communities.
- CXR-Clinical Dissociation: "Looks sicker on the film than in the bed" is the classic teaching.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.