WASHINGTON (Reuters) – Fewer US patients, especially children, are getting inappropriate antibiotics for coughs, colds and ear infections, according to a report published yesterday.

But the trend may be due as much to new respiratory vaccines such as Wyeth's Prevnar as to doctors following guidelines aimed at reducing unnecessary antibiotic use, Dr. Carlos Grijalva of Vanderbilt University in Tennessee and colleagues reported.

They found prescriptions for antibiotics for acute respiratory infections such as colds, flu, sore throats and ear infections fell by about a third between 1995 and 2006.

Visits to the doctor for such infections fell, too – especially for ear infections, which, like many coughs and colds, are often caused by viruses that cannot be treated with antibiotics.

"The decreases observed in antibiotic prescriptions in children younger than five years were largely related to decreases in otitis media (ear infection) visit rates," they wrote in the Journal of the American Medical Association.

At the same time, prescription rates for so-called broad spectrum antibiotics rose, which the researchers said suggested that doctors, parents and patients need to do more to limit unneeded use of antibiotics.

Infectious disease experts have been cautioning for years that the overuse of antibiotics has helped breed drug-resistant bacteria that need ever-stronger drugs to kill them.

Bacteria that are not killed right away by an antibiotic can thrive when a patient stops taking antibiotics – especially if the patient does not finish the full course or take a high enough dose.

These bacteria pass on their drug-resistant genes in a quick evolutionary change that now means penicillin and related drugs are useless against half of all US Staphylococcus aureus infections, for example.

Grijalva's team studied 12 years of US data on 6.2 billion hospital, doctor and clinic visits.

Among children under five, visits for acute respiratory infections fell by 17 percent, they found, while prescriptions for antibiotics for respiratory infections dropped 36 percent.

Visits for ear infections fell 33 percent and the use of antibiotics for ear infections fell 36 percent.

They said much of the reduction can be credited to influenza vaccines and to Prevnar, which was introduced in 2000 and has annual sales of more than $3 billion.

The vaccine currently protects against seven strains of Streptococcus pneumoniae and Wyeth is seeking approval for a vaccine that protects against 13 strains.

Just as many children over five and adults sought medical care for respiratory infections but the rate of prescribing antibiotics for them went down by 18 percent.

"Our results indicate that overall antibiotic prescription rates have decreased significantly.

"These changes coincided with efforts to reduce inappropriate antibiotic prescribing and the initiation of routine infant immunisation with pneumococcal conjugate vaccine," the researchers wrote.