Children who develop two types of brain cancer might have been infected with bacteria or a virus when they were babies, researchers suggested yesterday.

An analysis of more than 1,000 cases over 44 years in north west England has found a pattern in the diseases which appeared in clusters, suggesting an environmental factor such as an infection, might be responsible.

A team based at Manchester University noticed that children born in late autumn or winter had a higher risk of two forms of cancer, called astrocytoma and ependymoma, where tumours develop in supporting tissues of nerve cells and the brain. Scientists speculate this may be because children are more prone to infection in winter.

The two conditions account for nearly half the cases of childhood brain cancer which is diagnosed in 290 children each year and kills 100.

The Manchester group, funded by Cancer Research UK, found that in certain years more children who lived close together were diagnosed with cancer than would be expected by chance. This produced short lived mini epidemics at various times in different parts of the region, they reported in the British Journal of Cancer.

The pattern appeared to be typical of those linked to diseases caused by infection rather than other long lasting environmental factors, including pollution, which might be expected to produce clusters in one place over a longer time.

Some scientists have long argued that childhood leukaemia might be linked to exposure to radiation from nuclear power stations but the link has never been proved and bacteria and viruses have also been blamed for this and other types of cancer. Man-made viruses are also being used on patients to see if they can act as tumour-busting agents.

Jillian Birch, leading the Manchester team, said: "Our results indicate that environmental factors are involved in causing brain tumours in children and the most likely explanation for the pattern we have seen is that one or more types of infection are responsible.

"The fact that the space-time clusters and the seasonal pattern in births are restricted to particular types of childhood cancer adds weight to our findings and will allow us to focus our future research on these cases."

Sir Paul Nurse, joint director general of Cancer Research UK, said: "If infection is playing a role, this might lead to new ideas for preventing and treating this important disease."