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A sore, scratchy throat is often the first sign that you're getting sick, and it's a common reason people see their doctors. Most sore throats, such as those that accompany a cold or the flu, are caused by viral infections and usually go away on their own within a few days.

Only a small portion of sore throats are the result of strep throat. But it's important to identify this bacterial throat infection for a number of reasons. Unlike other causes of sore throat, strep throat is treatable. The bacteria that cause strep throat respond quickly to antibiotics, and treatment stops the infection from spreading to other people.

If not treated, strep throat infections can sometimes cause complications such as rheumatic fever. Rheumatic fever can cause painful and inflamed joints and a rash, and can even result in damage to heart valves. Another potential complication of strep throat infections is kidney inflammation.

Strep throat is most common in children between the ages of 5 and 15, but it affects people of all ages. In addition to throat soreness, signs and symptoms typically include a fever plus tender and swollen lymph glands (nodes) in the neck. Younger children may also complain of abdominal pain.

If you or your child has signs or symptoms of strep throat, see your doctor. A quick test can result in diagnosis of strep throat in most cases, so that treatment can start promptly.

In general, signs and symptoms of strep throat include:

• Throat pain
• Difficulty swallowing
• Red and swollen tonsils, sometimes with white patches or streaks of pus
• Swollen, tender lymph glands (nodes) in your neck
• Fever
• Headache
• Rash
• Stomachache and sometimes vomiting, especially in younger children

It's possible for you or your child to have many of these signs and symptoms, but not have strep throat. The cause of these signs and symptoms could be a virus, tonsillitis or other illnesses. That's why your doctor generally tests specifically for strep throat.

It's also possible to have the bacteria that cause strep in your throat without having a sore throat. Some people are carriers of strep, which means they can pass the bacteria on to others, but the bacteria no longer make them sick.

The cause of strep throat is bacteria known as Streptococcus pyogenes, or group A beta-hemolytic streptococcus.

Streptococcal bacteria are highly contagious. They can spread through airborne droplets when someone with the infection coughs or sneezes. You can also pick up the bacteria from a doorknob or other surface and transfer them to your nose or mouth. Kitchen utensils and bathroom objects are other common sources of infection transmission.

Strep throat occurs most commonly in children between the ages of 5 and 15.

Children with recurrent strep throat whose tonsils are intact are more than three times as likely to develop subsequent episodes of strep throat as are children who've had their tonsils removed, according to a 2006 Mayo Clinic study.

While strep throat can occur at any time of the year, it tends to circulate in late fall, winter and early spring. Strep bacteria flourish wherever groups of people are in close contact. That's why the infection spreads easily among family members, in schools and in child care settings.

Call your doctor if you or your child has any of these signs and symptoms:

• A sore throat without a cold or runny nose
• A sore throat accompanied by tender, swollen lymph glands (nodes)
• A sore throat that lasts longer than 48 hours
• A fever higher than 103 F in older children, or any fever lasting longer than 48 hours
• Rash
• Joint pain
• Problems breathing or difficulty swallowing anything, including saliva

Call your doctor if you or your child doesn't feel better after taking antibiotics for 24 to 48 hours. Sometimes problems occur even after you or your child has finished treatment for strep throat.

Call your doctor if your child develops a fever — or has pain or swelling in the joints, shortness of breath or a rash — after a strep infection, even as long as three weeks after a strep infection. These can be indicators of rheumatic fever. Cola-colored urine after a strep throat infection may indicate kidney inflammation.

Doctors usually diagnose the cause of a sore throat on the basis of a physical exam and lab tests. During the exam, your doctor looks for signs and symptoms of strep throat, such as fever and enlarged lymph nodes, and will probably use a tongue depressor to get a good look at the throat and tonsils.

He or she will check for redness, swelling and white streaks or pus on the tonsils. There also may be tiny red spots on the soft or hard palate — the area at the back of the roof of the mouth. Although these signs indicate an infection, there's no way to tell by just looking whether it's viral or bacterial. In fact, some viral throat infections look worse than infections caused by streptococcal bacteria.

For that reason, your doctor is likely to use one or more of the following tests to check for the presence of bacteria, including streptococcal bacteria:

• Throat culture. For this test, a sterile swab is rubbed over the back of the throat and tonsils to get a sample of the secretions. It's not a painful procedure, but it may cause brief gagging. The sample is then cultured in a laboratory for the presence of bacteria, but results may take as long as two days.
• Rapid antigen test. Because of the waiting period for a throat culture, your doctor may also order a rapid antigen test on the swab sample. This test can detect strep bacteria in minutes by looking for foreign substances (antigens) in the throat. If you or your child tests positive for strep bacteria, antibiotic treatment can begin right away. But rapid strep tests have a downside. They may miss some strep throat infections. For this reason, many doctors still use throat cultures, especially if results of the rapid test are negative.
• Rapid DNA test. Newer rapid tests use DNA technology to detect strep throat in a day or less from a throat swab. These tests are as accurate as throat cultures and the results are available sooner.

Although strep throat itself isn't dangerous, it may lead to serious complications if left untreated. These complications include other infections, such as:

• Tonsillitis or a collection of pus around the tonsils caused by infection (peritonsillar abscess)
• Sinus infection (sinusitis)
• Ear infection
• Scarlet fever, an illness characterized by a rash

Strep throat may also lead to inflammation of the kidney (glomerulonephritis) and rheumatic fever.

Rheumatic fever causes inflammatory deposits (nodules) to form in various tissues, including the joints, skin and muscles. These nodules also may form on the heart muscle, the lining of the heart and especially the heart valves, causing scarring that can interfere with the flow of blood inside the heart. Although surgery can sometimes repair scarred valves, the damage may be permanent. In some cases this damage may lead to heart failure. However, the risk of developing severe complications from strep throat is low in the United States.

If you or your child has strep throat, your doctor will likely prescribe an oral antibiotic such as penicillin, amoxicillin (Amoxil, Trimox), azithromycin (Zithromax), clarithromycin (Biaxin), clindamycin (Cleocin) or a brand of cephalosporin (Keflex, Ceclor). Penicillin may be given by injection in some cases — such as if you have a young child who is having a hard time swallowing or is vomiting from strep throat.

These antibiotics reduce the duration and severity of symptoms, as well as the risk of complications and the likelihood that infection will spread to classmates or family members.

Once treatment begins, you or your child should start feeling better in just a day or two. Call your doctor if you or your child doesn't feel better after taking antibiotics for 24 to 48 hours. If children on antibiotic therapy feel well and don't have a fever, they often can return to school or child care when they're no longer contagious — usually 24 hours after beginning treatment. But be sure to finish the entire course of medicine. Stopping medication early may lead to recurrences and serious complications, such as rheumatic fever or kidney inflammation.

In addition to antibiotics, your doctor may suggest ibuprofen (Advil, Motrin, others) or acetaminophen (Tylenol, others) to relieve throat pain and reduce fever. Because of the risk of Reye's syndrome, a potentially life-threatening illness, don't give aspirin to young children. Be careful with acetaminophen, too. Taken in large doses, it can cause serious problems. Talk to your doctor or pharmacist if you have questions.

Proper hand cleaning is the best way to prevent all kinds of infections. That's why it's important to clean your own hands regularly and to teach your children how to clean their hands properly, using soap and water or an alcohol-based hand sanitizer.

In addition, teach your children to cover their mouths when they cough or sneeze. And if you or your child does have strep throat, don't share drinking glasses or eating utensils. Wash those items carefully in hot, soapy water or in a dishwasher.

For some children who struggle with recurrent strep throat, removing the tonsils (tonsillectomy) may provide relief. The decision to remove a child's tonsils must be weighed against various factors, however, including the risks of anesthesia and bleeding after the procedure and missed school days to recover from the procedure.

In most cases, antibiotics will quickly wipe out the bacteria behind the infection. In the meantime, try these tips to relieve symptoms of strep throat:

• Get plenty of rest. Sleep helps your body fight infection. If you have strep throat, stay home from work if you can. If your child is ill, keep him or her at home until there's no sign of fever and he or she feels better.
• Drink plenty of water. Keeping a sore throat lubricated and moist eases swallowing. Drinking plenty of water also helps prevent dehydration.
• Eat soothing foods. Foods that are easy on a sore throat include broths, soups, applesauce, cooked cereal, mashed potatoes, soft fruits, yogurt and soft-cooked eggs. You may even want to puree foods in the blender to make them easier to swallow. Very cold foods such as sherbet, frozen yogurt or frozen fruit pops also may be soothing. Avoid spicy foods or acidic foods such as orange juice.
• Gargle with warm salt water. For older children and adults, gargling several times a day can help relieve throat pain. Mix 1/4 teaspoon of table salt in 8 ounces of warm water. Be sure to tell your child to spit out the liquid after gargling.
• Use a humidifier. Adding moisture to the air can help ease discomfort. Moisture keeps mucous membranes in your throat from becoming dry and even more irritated. Choose a cool-mist humidifier and clean it daily, because bacteria and molds can flourish in some humidifiers. Saline nasal sprays also help to keep mucous membranes moist.
• Stay away from irritants. Cigarette smoke can irritate a sore throat and increase the likelihood of infections such as tonsillitis. In addition, avoid fumes from paint or cleaning products, which can be irritating to your throat and lungs.
• Plan low-key activities for a sick child. If your child tests positive for strep throat, he or she should take antibiotics for at least 24 hours before returning to school or child care. When staying home with your child, plan some low-key activities that you both can enjoy. These can be things you don't normally have time to do, such as reading a favorite book aloud.