Although people often say they have "strep" throat, most sore throats actually are caused by a virus, not streptococcus bacteria, and shouldn't be treated with antibiotics, suggest guidelines published by the Infectious Diseases Society of America (IDSA). Antibiotics are ineffective against viruses.

The IDSA's newly revised guidelines for Group A streptococcal pharyngitis -- strep throat -- also advise that when a strep infection is confirmed by testing, it should be treated with penicillin or amoxicillin -- if the patient does not have an allergy -- and not azithromycin or a cephalosporin. Further, the guidelines recommend that children who suffer from recurrent strep throat should not have their tonsils surgically removed solely to reduce the frequency of infection. The guidelines are being published September 10 in the journal Clinical Infectious Diseases.

About 15 million people in the U.S. see the doctor for a sore throat every year and up to 70 percent receive antibiotics, although only a smaller percentage actually have strep throat: approximately 20 to 30 percent of children and just 5 to 15 percent of adults.

The guidelines note that children and adults do not need to be tested for strep throat if they have a cough, runny nose, hoarseness and mouth sores, which are strong signs of a viral throat infection. A sore throat is more likely to be caused by strep if the pain comes on suddenly, swallowing hurts and the sufferer has a fever without the above listed features, but should be confirmed through testing before antibiotics are prescribed, the guidelines note.

If strep is suspected, the guidelines recommend physicians use the rapid antigen detection test, which provides results in a few minutes. If that test is negative, a follow-up throat culture is recommended for children and adolescents, but not for adults. Results of the culture can take up to several days, but antibiotics should not be prescribed unless results are positive, the guidelines note. Because strep throat is uncommon in children three years old or younger, they don't need to be tested, the guidelines recommend.

"The guidelines promote accurate diagnosis and treatment, particularly in avoiding the inappropriate use of antibiotics, which contributes to drug-resistant bacteria," said lead author Stanford T. Shulman, MD, chief of the division of infectious diseases at Ann & Robert H. Lurie Children's Hospital of Chicago and professor of pediatrics at Northwestern University Fineberg School of Medicine. "We recommend penicillin or amoxicillin for treating strep because they are very effective and safe in those who are not allergic, and there is increasing resistance of strep to the broader-spectrum -- and more expensive -- macrolides, including azithromycin."

He notes the guidelines recommend against tonsillectomy for children with repeated throat infection except in very specific cases -- such as a child who has obstructive breathing -- because the risks of surgery are generally not worth the transient benefit.

Serious complications from strep throat -- particularly rheumatic fever -- have diminished in the United States, but occasionally do occur, so accurate diagnosis is key, Dr. Shulman said.

The voluntary guidelines are not intended to take the place of a doctor's judgment, but rather to support the decision-making process, which must be individualized according to each patient's circumstances.

The eight-member Group A streptococcal pharyngitis guidelines panel comprises experts representing a variety of specialties, including adult and pediatric infectious diseases physicians, pediatricians and respiratory diseases authorities. In addition to Dr. Shulman, the panel includes: Alan L. Bisno, Herbert W. Clegg, Michael A. Gerber, Edward L. Kaplan, Grace Lee, Judith M. Martin and Chris Van Beneden.

IDSA has published more than 50 treatment guidelines on various conditions and infections, ranging from HIV/AIDS to Clostridium difficile. As with other IDSA guidelines, the Group A strep pharyngitis guidelines will be available in a smartphone format and a pocket-sized quick-reference edition. A podcast with the lead author and the full guidelines are available free on the IDSA website at www.idsociety.org.

Note: The guidelines are available online.