Influenza

Influenza is a highly contagious respiratory illness caused by influenza A or B viruses.

• Seasonal outbreaks during winter months.
• Pandemics can occur with new viral strains (e.g., H1N1 in 2009).

• Respiratory droplets: coughing and sneezing.
• Direct contact: contaminated surfaces.

• Rapid onset.
• Fever and chills.
• Muscle aches and fatigue.
• Cough (usually dry).
• Sore throat.
• Headache.
• Rhinorrhoea (runny nose).

• Coryza.
• Dry cough.
• Small volume lymphadenopathy.

• Combined nose and throat swab: PCR for virus detection.
• Chest X-ray: if viral pneumonia is suspected or severe disease (influenza can cause a pneumonitis).
• Blood tests: leukopenia, elevated CRP.

• Supportive care: rest, hydration, antipyretics.
• Antivirals: oseltamivir or zanamivir may reduce the duration of symptoms if started within 48 hours of symptom onset.
• Antibiotics only if secondary bacterial infection is suspected.

• Annual vaccination, especially for high-risk groups (elderly, healthcare workers, chronic medical conditions).
• Hand hygiene and respiratory etiquette (covering mouth/nose when coughing/sneezing).
• Isolation of infected individuals.

• Secondary bacterial pneumonia: commonly caused by Staphylococcus aureus or Streptococcus pneumoniae.
• Myositis and rhabdomyolysis.
• Encephalitis and neurological manifestations (rare).
• Myocarditis and pericarditis.
• Otitis media: especially in children.

• Influenza is a highly contagious respiratory illness caused by influenza A or B viruses.
• Often presents with general systemic features such as muscle aches, fever and malaise along with coryzal symptoms.
• Investigation is primarily through a combined nose and throat swab to detect virus.
• Management is primarily supportive, alongside antivirals and antibiotics if appropriate.
• Prevention is important to prevent severe infection in high risk individuals.