Infectious Diseases Conference 2019

Facts about flu

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What are the symptoms? 

Common clinical symptoms for both influenza A and B may present with sudden onset of fever, cough, sore throat, myalgia/myositis, fatigue, and gastrointestinal (GI) presentations such as vomiting and diarrhoea. Fever is more common in children than in adults. Although clinical presentations are indistinguishable between influenza A and B infections, some studies report differences by age groups. Influenza A tends to cause more severe illness, although influenza B can be severe in children. In adults, influenza B infections more frequently present with vomiting, diarrhoea, abdominal pain, headache, general weakness and rhinorrhoea compared to influenza A. It was found that cases with influenza B infection presented more with upper respiratory tract infections, myosotis and gastroenteritis compared to influenza A in children. Without a test, however, you cannot prove influenza infection, as there are over 90 other cold and cough viruses which circulate in winter.  However, when an epidemic of flu is occurring, flu-like illness is more likely to be flu.

How does it spread?  

Influenza infection can be transmitted through droplets, aerosol and direct contact with the infected person. Whilst droplet is the main mode of spread, numerous studies have documented airborne transmission. In one US study, viable influenza virus was detected in the air of the emergency department 3 hours after the infected patient had left.

Who is affected?  

Influenza infects all ages, with peaks at the extremes of age – the very old and the very young. In 2017 the peak has been in older adults >80 years and over and children 5-9 years.  Males and females are equally affected. Up to a quarter of people can get infected in a severe epidemic.

What are the complications? 

Influenza can result in primary viral pneumonia, which occurs early in the course of illness, or secondary bacterial pneumonia, with onset later (1-2 weeks after initial symptoms). Bacterial pneumonia is the most common influenza-associated complication, especially in children and the elderly. Bacterial infection can be complicated by antibiotic resistance and there is are vaccines available for the most common bacterial complication, pneumococcal infection. Unfortunately, despite being provided free to people over 65 years and other risk groups, rates of vaccination against pneumonia are low. Other complications can be worsening of asthma and respiratory diseases and exacerbation of underlying comorbidities in persons who are at risk of the infection. Heart failure, precipitation of heart attacks and sinusitis may also occur. Occasionally encephalitis and complications of other organ systems may occur.

Influenza vaccine: 

Primary prevention is with vaccination with influenza vaccine annually. The mutation of the virus year to year requires annual vaccination. The vaccine is safe and effective, but effectiveness can vary depending on how well the vaccine is matched to circulating strains. People aged 65 years and over, and those with medical or other risk factors are recommended and funded for a free vaccine in Australia. The quadrivalent vaccine, introduced in 2016, allows protection against four strains, which gives better effectiveness against flu.  Research is underway for a universal flu vaccine which will remove the need for an annual jab.

Other prevention & control measures: 

Neuraminidase inhibitors (NAIs) can be used as prophylaxis or treatment, and when used as prophylaxis can curtail outbreaks.  Cough etiquette, hand hygiene and infection control measures are also vital to prevent further spread of infection. Personal protective equipment such as masks is recommended for healthcare workers. Guidelines recommend “droplet precautions” for seasonal influenza, however, airborne transmissions well documented for influenza.