Microbiology
Pathogens
Regarding influenza, which of the following statements is CORRECT:
Answer:
Inactivated viral vaccines are prepared annually based on predictions of the strain most likely to be prevalent and are recommended annually for certain patients including people over 65 years of age, pregnant women and people with chronic disease or immunosuppression (e.g. post-splenectomy). Transmission of influenza is via the respiratory droplet or direct contact spread. Treatment is generally supportive. In patients who are at particular risk of complications, influenza can be treated with neuraminidase inhibitors zanamivir and oseltamivir, which decrease severity and shorten the duration of symptoms. Antigenic shift, not drift results in influenza pandemics.Influenza
Microbiology / Pathogens / Respiratory Viruses
Last Updated: 21st April 2019
Epidemiology
Antigenic drift occurs via gradual genetic change allowing the virus to change its surface antigens, undermining previous humoral immunity and thus resulting in seasonal epidemics (in winter in the UK).
Antigenic shift is where different strains of a virus combine via genetic reassortment to form a new subtype with new antigens (e.g. human with avian or pig influenza strains) and this can result in pandemics. Pandemics typically occur every 10 - 40 years.
Transmission
Transmission is by respiratory droplet spread or direct contact with respiratory secretions of someone with the infection. The incubation period lasts 1 - 4 days and patients are infectious for about 3 days, starting 1 day before symptoms emerge.
Clinical Features
Clinical features usually include headache, myalgia, fever and cough, lasting for 3 - 4 days.
Complications
Complications include:
- primary viral or secondary bacterial pneumonia (more common in the elderly and in patients with cardiopulmonary disease, S. aureus commonly implicated)
- exacerbations of asthma and COPD
- myocarditis
- encephalitis
- meningitis
- otitis media
- sinusitis
- febrile convulsions
Diagnosis
Diagnosis is usually clinical. Rapid laboratory diagnosis can be made with direct immunofluorescence or NAAT detection.
Treatment
Treatment is usually supportive. In patients who are at particular risk of complications, influenza can be treated with neuraminidase inhibitors zanamivir and oseltamivir, which decrease severity and shorten the duration of symptoms.
Prevention
Inactivated viral vaccines are prepared annually based on predictions of the strain most likely to be prevalent and are recommended annually for certain patients including:
- people over 65 years old
- healthcare professionals
- pregnant women
- people with chronic disease e.g. cystic fibrosis, renal disease, heart disease, asthma
- immunocompromised individuals e.g. asplenism, HIV/AIDs, chemotherapy
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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 |
