Microbiology
Infections
Question 176 of 180
A 24-year-old pigeon fancier presents with fever of 40°C, severe diffuse headache, malaise, dry hacking cough and muscle aches. Lung exam reveals bilateral crackles and there is hepatosplenomegaly. Which of the following is the most likely infective pathogen:
Answer:
Chlamydia psittaci infects birds and many mammals. Humans are infected primarily by inhaling organisms in dry bird faeces. Psittacosis may be asymptomatic or may produce high fever and pneumonia associated with headache, altered mental state, and hepatosplenomegaly.Pneumonia
Microbiology / Infections
Last Updated: 19th January 2020
Infective Agents
- Community acquired pneumonia
- Streptococcus pneumoniae (most common)
- Haemophilus influenzae
- Staphylococcus aureus
- Hospital acquired pneumonia (develops at least 24 hours after hospital admission)
- Gram-negative bacilli e.g. Escherichia coli and Klebsiella pneumoniae
- Pseudomonas aeruginosa
- Staphylococcus aureus
- Atypical pneumonia
- Mycoplasma pneumoniae
- Legionella pneumophila
- Chlamydophila pneumoniae
- Chlamydophila psittaci
Clinical Features
- Symptoms
- Systemic features: fever, myalgia, arthralgia, rigors, headache
- Cough (+/- productive)
- Dyspnoea
- Pleuritic chest pain
- Signs
- Dull percussion note over infected area
- Reduced chest expansion on affected side
- Bronchial breathing
- Crackles
- Increased tactile fremitus and vocal resonance
- Tachypnoea and tachycardia
Specific Pneumonias
- Mycoplasma pneumoniae
- More common in younger patients (school age and young adults)
- Outbreaks occur approximately every 4 years in the UK
- Flu-like illness followed by dry cough associated with extrapulmonary complications such as erythema multiforme and SJS, autoimmune haemolytic anaemia, pericarditis and myocarditis, meningoencephalitis
- Legionella pneumophila
- Outbreaks among patients staying at institutions with contaminated water tanks
- Flu-like illness before developing a dry cough and shortness of breath, associated with renal failure, gastrointestinal upset, confusion and hyponatraemia
- Chlamydia psittaci (psittacosis)
- Linked with exposure to infected birds
- Flu-like illness, dry cough, high temperature, photophobia and neck stiffness
- Klebsiella pneumoniae
- Associated with older patients, diabetes mellitus and alcoholism
- Sudden onset flu-like illness, high fever and productive cough with blood-tinged sputum (red currant jelly sputum)
Diagnosis
- Chest x-ray – consolidation +/- pleural effusion
- Sputum for M, C & S
- Urinary antigens for L. pneumophila and M. pneumoniae
- Blood cultures
- Bloods (FBC, U&Es, LFTs, CRP)
- Serology for atypical organisms
Assessment of CAP
In adults, severity is assessed by clinical judgement guided by mortality risk score (CURB65):
- Confusion (abbreviated mental test, AMT score ≤ 8)
- Urea (> 7 mmol/L)
- Respiratory rate (≥ 30/min)
- Blood pressure (< 90 systolic or ≤ 60 diastolic)
- 65 (age ≥ 65 years)
Patients are stratified for risk of death as follows:
- 0 or 1: low risk (less than 3% mortality risk)
- 2: intermediate risk (3‑15% mortality risk)
- 3 to 5: high risk (more than 15% mortality risk).
Treatment of CAP
Use clinical judgement in conjunction with the CURB65 score to guide the management of community‑acquired pneumonia, as follows:
- consider home‑based care for patients with a CURB65 score of 0 or 1
- consider hospital‑based care for patients with a CURB65 score of 2 or more
- consider intensive care assessment for patients with a CURB65 score of 3 or more.
| Infection | First Choice Antibiotic |
|---|---|
| Low-severity community acquired pneumonia |
|
| Moderate-severity community acquired pneumonia |
|
| High-severity community acquired pneumonia |
|
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
