A 61-year-old Professor of Microbiology develops a high fever with muscle aches and pains and coryzal symptoms 2 days after returning from Shanghai, where he had travelled in the countryside and then attended a large infectious diseases conference. On examination he is flushed, with a temperature of 39.7 °C and tachycardic, but not in any respiratory distress.
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1. What is the differential diagnosis?
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In any fever in a returning traveller it is important to exclude malaria. Other possibilities in this case include influenza, and other respiratory viruses, and enteric fever.
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2. What investigations will you carry out?
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Chest X-ray, full blood count and white cell differential, C-reactive protein, Nasopharyngeal aspirate for detection of respiratory viruses, urine analysis followed by culture if blood/nitrates are present, sputum culture and blood cultures.
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3. The NPA is positive for Influenza A. What else do you need to know about this organism?
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Influenza A strains have surface neuraminidase and haemagglutinin molecules. Typing of these is important for the detection of emerging strains to which there is little immunity in the population. Major shifts are associated with pandemics that may have a high mortality.
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4. How do new strains of Influenza A emerge?
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Strains of Influenza A from different animal hosts (e.g. birds or swine) are able to exchange genes that code for different haemagglutinin or neuraminidase molecules. For example, H5N1 is thought to have emerged from birds in South East Asia in 2004. H1N1, a strain of swine 'flu, caused a pandemic in 2009.
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5. How should patients with ’flu be treated?
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Many patients will improve spontaneously with symptomatic treatment only (aspirin/paracetamol and fluids); however, in the immunocompromised or those with severe disease and respiratory symptoms Tamiflu (oseltamivir) or Relenza (zanamivir) can shorten the course of infection. Secondary bacterial infection should be treated promptly with an agent that is active against Staphylococcus aureus.
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6. How is 'flu prevented?
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Influenza viruses are spread by respiratory droplets dispersed when talking, sneezing and coughing. High efficiency respiratory masks will help protect healthcare workers and negative-pressure ventilation will protect other patients from exposure.
The mainstay of prevention is vaccination but this needs to be with a vaccine that incorporates the circulation strains (haemagglutinin and neuraminidase type). Prophylaxis with either oseltamivir or zanamivir can also be used for known contacts.
