Common infections that affect mothers and babies may trigger certain types of childhood cancers, researchers said on Monday.

They found that leukemia and brain tumors, leading cancers in children, occurred in clusters, which suggests that outbreaks of infections are a contributing cause of the disease.

“We found that place of birth was particularly significant, which suggests that an infection in the mother while she is carrying her baby, or in a child’s early years, could be a trigger factor for the cancer,” said Dr. Richard McNally, of the University of Newcastle upon Tyne in northern England.

“These could be minor, common illnesses…such a cold, mild flu or a respiratory infection,” he added in a statement.

McNally and a team of researchers from England and Scotland, who reported the findings in the European Journal of Cancer, said the results could improve understanding about how cancer develops and may lead to better prevention and treatment.

Although cancer in children is rare, rates of the disease in youngsters in Europe have increased over the past three decades. Survival rates however have improved. Five-year survival rates are about 75 percent in western Europe and 63 percent in eastern Europe.

Leukemia is the most common childhood cancer, accounting for nearly one third of all cases. Most of the rise has been in children ages 1 to 4.

The researchers believe an infection in the womb or early in life could lead to cancer in young people who carry mutant cells that would make them more vulnerable to the disease.

“The virus would hit this mutant cell and cause a second mutation, prompting the onset of cancers like leukemia or brain tumors,” said McNally.

The findings are based on a statistical analysis of data from the Manchester Children’s Tumour Register, which recorded all cases of childhood cancers diagnosed between January 1954 and December 1998.

They looked for unusual patterns of cancer linked to the time and place of children’s birth and where they were living when diagnosed with cancer.

In some clusters they found 8 percent more cases of leukemia than would normally be expected and a 13 percent above-average incidence of the brain tumour astrocytoma.

“These findings provide more clues to a link between viruses and some types of childhood cancer, but we need more evidence before we can be sure,” said Professor John Toy, of the charity Cancer Research UK, which funded the research.