Everything you need to know about 8 common illnesses

1. Cold

The term "cold" is often a catchall for any mild respiratory infection, Smith writes.

"We recognize it as being sort of the fallback diagnosis," said Stuart Ray, a professor in the division of infectious diseases at Johns Hopkins Medicine.

Cold symptoms commonly involve a sore throat, cough, runny nose, congestion, and sometimes headache and fatigue. Symptoms like fever, muscle aches, and lower respiratory symptoms like shortness of breath or wheezing, can mean your infection is something more serious like the flu or respiratory syncytial virus (RSV).

You're most contagious with a cold when you feel the worst, which is often during the second and third days of symptoms, Smith writes. Typically, it's safe to assume you're not as contagious after day three or four, according to Patricia Whitley-Williams, a professor of pediatrics at the Rutgers Robert Wood Johnson Medical School.

If you still have a cough, you don't need to worry, Ray said, as your airways can remain inflamed from your body's immune response rather than the virus.

There are no antiviral treatments for the common cold, but there are over-the-counter medicines that can help relieve symptoms as well as some home remedies.

2. Conjunctivitis (pink eye)

Conjunctivitis, also known as pink eye, generally refers to inflammation of the conjunctiva, which is the mucus membrane lining the skin around your eyeball. It is most often caused by viruses in the adenovirus family, however, there are some less common bacterial forms of conjunctivitis as well, Smith writes.

Symptoms include itchy, red, and weepy eyes and typically last between two to seven days. However, adenoviruses can spread from one eye to the other, so it's possible to have pink eye for two weeks.

"Bacterial conjunctivitis, more classically, is just one eye," said Lori Handy, an infectious disease physician at Children's Hospital of Philadelphia. "Viral conjunctivitis, more classically, is both eyes because it's so contagious that it's hard to protect one eye from the other."

As long as you have conjunctivitis in some form, you're contagious, Smith writes. The best way to prevent spreading it is to stay home until your symptoms are gone, avoid touching your eyes, and be diligent about washing your hands.

If you believe you or your child has pink eye, you should see a doctor to determine what kind it is, according to Handy.

"This is one infection where I do really advocate for talking with your healthcare provider, because the counseling is very different based on what type you have, as is the treatment," Handy said.

There isn't a treatment to get rid of viral conjunctivitis, but you can use a damp compress to help with symptoms. Bacterial conjunctivitis, however, can be treated with antibiotic ointment or drops.

3. COVID-19

COVID-19 is caused by the SARS-CoV-2 coronavirus and most common symptoms including sore throat, congestion, fatigue, fever, and cough.

Rapid COVID-19 tests are still the best way to determine whether you have the disease, Smith writes. If you test negative at first, try again 48 hours later, as it's possible you didn't have enough virus in your nose for your first test to detect the disease.

Symptoms typically resolve in a week for most people, however, some can have longer infections that stick around for weeks or even develop into long COVID.

According to the CDC, you can go out in public after your fifth day of COVID-19 symptoms provided you're fever free, though the agency advises you wear a mask for another five days to minimize your risk of spreading the virus to others.

"COVID is no longer infectious in the second week," said Ray. "But the variability is still there." For example, if your case of COVID-19 is moderate or severe and you're experiencing shortness of breath or need to be hospitalized, you should isolate for 10 days. "The more severe the infection, the more protracted the infectiousness," Ray said.

You can treat COVID-19 early with the antiviral Paxlovid within the first five days of infection. Vaccines against the disease are also effective at preventing hospitalization and death. For symptom relief, over-the-counter cold medicines can help.

4. Flu

The seasonal flu is caused by two types of viruses: influenza A and influenza B. Both viruses can circulate at the same time, but one type generally dominates each season.

It can be difficult to tell whether you have the flu or another respiratory virus, but tests are available at pharmacies or doctors' offices. Currently, there are no at-home flu tests available in the United States.

Flu symptoms typically include sore throat, runny nose, congestion, and cough. Fatigue, fever, headache, and muscle aches are also common symptoms, and some people experience vomiting or diarrhea.

The easiest way to determine if you have the flu is to consider how quickly symptoms arrived and how bad you feel. "If you feel much sicker than you have with other colds, then be thinking about flu," Ray said.

People with the flu typically feel their worst for three days before symptoms begin to taper off.

Experts say you're contagious with the flu for around five days and at your most contagious during the first three days of symptoms.

"If I got the flu Monday, by Friday I'm probably not very infectious for others," said Edward Walsh, a professor of medicine at the University of Rochester and head of infectious diseases at Rochester General Hospital.

After five days, "if you're starting to feel better, you'll probably not have as much virus in your nose," said Seema Lakdawala, an associate professor of microbiology and immunology at Emory University School of Medicine. However, if your symptoms are lingering or if you're going to see somebody at a high risk for severe infection, you should wait another few days or wear a mask.

The best way to treat the flu is to get the annual flu shot. Antiviral treatments like Tamiflu can help minimize symptoms, but they need to be taken within the first few days of illness. Home remedies and over-the-counter medications can also help relieve symptoms.

5. Hand, foot, and mouth disease

Hand, foot, and mouth disease is caused by viruses within the enterovirus family and is most common in children under the age of five, though it can also be contracted by adults.

Symptoms of the disease typically include a rash on the hands and feet and sores in the mouth. Children also typically develop a fever. These symptoms are usually their worst in the first two to three days and resolve after about a week.

The rash will usually look like small red bumps that sometimes contain fluid. Meanwhile, the mouth sores are usually on the gums or tongue and can prevent children from eating or drinking.

People are most contagious with hand, foot, and mouth when symptoms first arrive. Once the fever subsides for 24 hours, the mouth sores are mostly gone, and the rash begins to heal, children can return to school.

"I wouldn't be cavalier about it and send your child to school sick," Handy said. "If they're past those acute symptoms, they're then at the point where they have a lower likelihood of spreading," she added.

There aren't any treatments to cure hand, foot, and mouth disease, but taking fever reducers and painkillers like acetaminophen or ibuprofen can help. For children, Handy recommends cold, soft foods like ice pops and yogurt that won't irritate their mouth sores.

6. Norovirus

Norovirus symptoms typically come on quickly, last one to two days, and include diarrhea, vomiting, nausea, and stomach pain.

People are contagious with norovirus for weeks after their symptoms subside, though viral levels aren't as high as when you first become sick. Once you're no longer experiencing diarrhea or vomiting, you can return to work or school, though it's important to continue being vigilant about washing your hands after you use the bathroom.

There's no treatment for norovirus, and doctors typically recommend against seeing them when you have a stomach bug as there isn't much that can be done and you could spread the virus to other patients, according to Ferric Fang, a professor of laboratory medicine and microbiology at the University of Washington School of Medicine.

The main priority with norovirus is prevent dehydration, which you can do by having drinks that contain electrolytes like Gatorade or Pedialyte.

7. RSV

RSV can often be dismissed as another mild version of the common cold, but it can prove very serious in infants and older adults.

Symptoms include a runny or stuffy nose, cough, headache, and a fever. Experts say that RSV is more likely to affect the lungs and lower respiratory tract, which can lead to severe coughing, wheezing, and shortness of breath.

Symptoms typically last around a week, though a cough can linger beyond that.

Similar to other respiratory viruses, the first few days of symptoms are the most contagious with RSV, and viral levels drop around day five. After that, it's safe to assume you're not contagious anymore, provided you don't have a fever and aren't producing a lot of mucus.

There aren't any antiviral treatments for RSV, but over-the-counter medications and home remedies can help with symptoms. Currently, there are two vaccines for RSV for adults ages 60 and older that can protect against a severe case of the disease. There's also a vaccine approved for pregnant women in their third trimester so antibodies can be passed on to their newborns. Additionally, there's a new preventive therapy that uses monoclonal antibodies to protect infants from a severe case of RSV.

8. Strep throat

Strep throat is caused by Group A streptococcus, a bacteria with nearly 100 strains in existence that can cause a variety of diseases, including scarlet fever and skin infections.

Symptoms of strep throat include a very sore throat, white film in the back of the throat, and sometimes a fever. You can be tested for strep at a doctors' office with a throat swab.

Strep throat can be treated quickly and easily with antibiotics like penicillin or amoxicillin, and once that treatment begins, bacteria die off quickly and a person with strep is no longer contagious within about 24 hours.

"Most kids can return to school within the next 12 to 24 hours, as long as they're otherwise doing well: fever-free, eating drinking OK," said Handy.

It's important to get strep treated quickly, as the bacteria could cause other, more severe infections, like cellulitis, impetigo, scarlet fever, or rheumatic fever. In severe and rare cases, streptococcus bacteria can lead to a blood infection, bone infection, septic shock, or necrotizing fasciitis.

It's important to note these are more severe cases "not to scare parents," Handy said, but added that parents need to ensure they get their children treated quickly and "if symptoms worsen, they get medical attention quickly." (Smith, New York Times, 10/6)

As the United States heads into the fall and winter, CDC predicts the country will see a "moderate COVID-19 wave" and a "typical" flu and respiratory syncytial virus (RSV) burden, similar to last year, Shannon Firth writes for MedPage Today.