Is Strep Throat Contagious? Here's How It Spreads and How to Prevent It

When your kid starts to complain that their throat hurts when they swallow (or you've got the same symptom), your first thought might be strep throat.

Strep throat is a throat and tonsil infection caused by group A Streptococcus bacteria‌.‌ It's different from a cold, which is usually caused by a virus. But just like the common cold, strep can spread like wildfire, especially among kids.

"As with other airborne [illnesses], strep is highly contagious," says Louis Morledge, MD, an internist at Northwell Lenox Hill Hospital in New York City.

In addition to throat pain, strep can cause a fever and swollen tonsils, often covered in white patches. Some people with strep also get a stomachache, nausea or vomiting, or a spotty red rash (especially under the arms), per the American Academy of Family Physicians. Unlike a cold, it doesn't usually cause a cough or a runny or stuffy nose.

Strep travels from one person to the next through tiny respiratory droplets that contain strep bacteria. If you're near an infected person when they cough or sneeze, you can catch strep by breathing in the bacteria-laden droplets, Dr. Morledge explains.

The droplets can also land on surfaces (like doorknobs, keyboards or faucet handles). If you touch the infected surface and then touch your mouth, nose or eyes, the bacteria can make you sick, he adds. Sharing cups, utensils or plates with someone who's infected can spread strep, too.

People often spread strep without realizing it. That's because while the infection takes two to five days to cause a sore throat and other symptoms, you can transmit the bacteria to others even before you feel sick, according to the Centers for Disease Control and Prevention (CDC).

It can take up to five days to start having symptoms after catching strep. Once you start to feel sick, it can take seven to 10 days for your symptoms to fully clear with treatment, per the Cleveland Clinic.

That said, you'll notice a big improvement within 12 to 24 hours of starting antibiotics (like amoxicillin), which are typically prescribed for bacterial infections like strep. Once you've passed that benchmark and no longer have a fever, you're in the clear to go back to school or work, per the CDC.

Most doctors prescribe a 10-day course of antibiotics for strep. Even though you'll feel better after the first day, it's important to keep taking your meds until they're finished to completely kill off the infection and keep your symptoms from coming back, according to the Mayo Clinic.

You'll stay sick — and contagious — for much longer without antibiotics, though. "Untreated individuals can be contagious for up to four weeks" after becoming infected, says Donna Casey, MD, an internal medicine physician at Texas Health Presbyterian Hospital Dallas.

You're significantly less contagious once you've been on antibiotics for 24 hours and no longer have a fever. But even after crossing that threshold, it's still possible to spread strep. "Antibiotics can reduce transmission up to 80 percent after 24 hours of therapy," Dr. Casey says.

It's OK to go back to work or school after the 24-hour mark (as long as you're also fever-free), according to the CDC. But you might want to hold off on close contact with people at higher risk of complications from infections (like newborns, older adults or those who are immunocompromised). "As I remind my patients, you're contagious until you finish the full course of medicine," Dr. Morledge says.

Though strep is highly contagious, there are a few things you can do to stay healthy and avoid spreading your germs if you do get sick.

Most importantly, be fastidious about washing your hands, especially after coming in contact with high-touch surfaces like doorknobs or faucets, or after caring for a sick family member.

"I suggest to all my patients to double down on hand hygiene during the winter months. Wash hands more frequently than at other times of year and carry antibacterial hand sanitizers for when you cannot access soap and warm water," Dr. Morledge says.

Try not to touch your mouth, nose or eyes, either. "All it takes is a second to touch an infected surface and then your face to transmit the bacterium to yourself," Dr. Morledge says.

Finally, limit your contact with sick people as much as you can, Dr. Casey recommends. You probably can't avoid your sick spouse, roommate or child entirely, but you can take a sick day or reschedule that coffee date or dinner party if someone in your household is feeling under the weather.

Here's some more helpful info about strep.