The chance of a child being infected by a resistant bacteria is directly related to the amount of antibiotics he or she has taken over the years, according to a study in the British Medical Journal. If these drugs are to retain any of their clinical usefulness, new prescribing policies are needed now, the authors warned.

The research team identified 461 children, under age four, living in Canberra, Australia to take part in the study. Parents were asked to keep a daily diary of the children's respiratory symptoms, visits to the doctor, and use of drugs, for two years. Nasal swabs were collected from the children every six months, and pneumococci bacteria were identified and tested for antibiotic resistance.

A total of 631 pneumococcal isolates were found, of which 14% were resistant to penicillin. The likelihood of carrying penicillin-resistant bacteria was doubled in children who had taken a "B lactam" antibiotic in the two months before each swab collection. The odds of carrying penicillin resistant bacteria was four percent higher for each additional day of B lactam use in the six months before swab collection.

The results suggest that a substantial reduction of this type of antibiotic use in preschool children could quickly reduce the rates of penicillin- resistant bacteria, said the study's authors. This is particularly important because these organisms tend to spread quickly among children in the community.