Intimate kissing with multiple partners almost quadruples a teenager's risk of developing meningitis, research suggested today.
Young children and adolescents face the greatest risks of meningococcal disease, which can cause serious disability and death.
Now researchers have found that, in teenagers, kissing is a major factor is helping the disease spread.
Rates of meningitis - which is the inflammation of the lining around the brain and spinal cord - increased significantly in England and the US in the 1990s.
The latest research, published in the British Medical Journal, examined possible risk factors in youngsters aged 15 to 19 who were admitted to hospital with meningococcal disease in six regions of England between January 1999 and June 2000.
The team, including researchers from the Institute of Child Health in London and the Health Protection Agency, took blood samples and nose and throat swabs, as well as asking about potential risk factors for meningitis.
The researchers confirmed previous findings that a history of illness preceding an attack of meningitis was linked to an increased risk.
Those who were students, and so mixing with large numbers of young people, were also at a greater risk.
"Kissing on the mouth has been suggested to be a risk factor," the researchers said.
"Intimate kissing has been shown to be a risk factor for the carriage of meningococci in university students and it is likely that intimate kissing with multiple partners increases the risk of transmission."