Tiny organisms in a child's nose could offer clues to improving the diagnosis and treatment of severe lung infections, a new study suggests.

The study found that the composition of the microbiome -- bacteria and viruses found in vast numbers in the body -- was altered in the noses of children with respiratory infections, compared with his healthy peers. This difference predicted how much time children had to spend in hospital and helped spot those likely to recover naturally, potentially reducing the need for antibiotics, said researchers from the University of Edinburgh.

"Our findings show, for the first time, the total microbial community in the respiratory tract -- rather than a single virus or a bacteria -- is a vital indicator of respiratory health. This could impact how doctors diagnose LRTIs and use precious antibiotics to fight infections," said lead author Debby Bogaert, Professor at the varsity.

Lower respiratory tract infections (LRTIs), including pneumonia and bronchiolitis, are a leading cause of death. Symptoms include, shortness of breath, weakness and fever. It was found that the microbiome in the back of the nose and throat was related to that seen in the lungs, making it easier to understand and diagnose infections.

For the study, published in The Lancet Respiratory Medicine, the researchers studied more than 150 children under the age of six, hospitalised with LRTI. They compared them with 300 healthy children. Children with LRTI had a different microbiome profile -- including the types and amounts of individual viral and bacterial organisms -- compared with the healthy children.

These profiles could identify 92 per cent of children as being healthy or ill when combined with factors like the child's age. This was true no matter what symptoms the child had. Experts say this breaks with traditional thinking that symptoms predict whether either a virus or bacteria is causing the illness and could impact a decision of whether or not to use antibiotics.