Microbiology
Pathogens
A 9 month old baby is brought into the ED with a one day history of wheezing and dyspnoea. She is having difficulty feeding due to her breathing. She is febrile, with tachypnoea, wheeze and intercostal and subcostal recession. On auscultation you note fine end-inspiratory crepitations. What is the most likely causative pathogen:
Answer:
The patient most likely has acute bronchiolitis, which is most commonly caused by respiratory syncytial virus (RSV).Respiratory Syncytial Virus (RSV)
Microbiology / Pathogens / Respiratory Viruses
Last Updated: 21st April 2019
Epidemiology and Transmission
Respiratory syncytial virus predominantly infects children during the first 3 years of life, with annual epidemics in the winter months. It spreads easily in the hospital environment, and in the elderly, frail or in those with respiratory tract disease. Transmission is via the respiratory droplet route and the incubation period is about 4 - 5 days.
Clinical Features
It initially presents with coryza, and in 40% of cases bronchitis develops in older children and bronchiolitis in the very young (most commonly 2 - 6 months). Infants with bronchopulmonary dysplasia or congenital heart disease are at particularly high risk.
Children with bronchiolitis are febrile and tachypnoeic with a dry cough and difficulty feeding. Examination may reveal chest hyperinflation, respiratory distress, wheezing and fine end-inspiratory crepitations. Chest x-ray may show hyperinflation and increased peribronchial markings (although CXR should only performed if there is diagnostic uncertainty or an atypical course).
Diagnosis
Diagnosis is usually clinical. Rapid laboratory diagnosis can be made with immunofluorescence, ELISA, NAAT or viral culture of nasopharyngeal aspirate.
Treatment
Most infants with acute bronchiolitis will have mild self-limiting illness and can be treated at home. Severe disease can develop quickly but with appropriate supportive treatment (humidified oxygen, nutrition and fluid support), mortality is low. Severely ill or immunocompromised patients may benefit from aerosolized ribavirin.
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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 |
