A potentially deadly respiratory virus that few people even know exists is surging in Australia, with at least 1,168 people infected last week in NSW alone. Human metapneumovirus (HMPV) can cause upper and lower respiratory disease in all age groups, but it poses a greater danger to young children, older adults and people with weakened immune systems. Though it usually causes a mild infection similar to the common cold - with nasal congestion, coughs, shortness of breath and a fever - complications can lead to bronchitis or pneumonia and can be fatal, especially among those who are immunocompromised, such as...