If you test positive for coronavirus or were exposed to someone who has, when could symptoms start, how long are you contagious, how long should you quarantine for and when should you get tested?

With COVID cases slowly rising in Illinois and parts of the U.S., local health officials have issued warnings to take precautions, particularly in areas where transmission risk is increasing.

As of the latest update, four counties in Illinois are currently under medium transmission risk, including DuPage County in the Chicago area.

Illinois has seen new cases of the virus increase by more than 40% in the last week.

According to the latest data from the Illinois Department of Public Health, the state is seeing an average of 3,136 new cases per day over the last seven days. That represents an increase of 43.1% in the last week. Over the last month, daily case rates in the state have increased by 170%, according to IDPH data.

Still, officials say that hospitalization metrics have not seen similar climbs.

Here's a look at the guidance from the Centers for Disease Control and Prevention on what to do if you test positive or believe you were exposed to someone who has. This guidance was most recently updated at the end of March.

According to the CDC, COVID symptoms can appear anywhere from two to 14 days after someone is exposed to the virus.

But guidelines state those who were exposed should watch for symptoms until at least 10 days after the last close contact with someone who had COVID.

Anyone with symptoms should get tested.

As BA.2 cases continue their dominance across the Midwest and U.S., here's a look at the latest symptoms to watch for.

Regardless of symptoms or vaccinations, those who are exposed to someone with coronavirus should get tested at least five days after their exposure.

Those who develop symptoms should get tested as symptoms develop, but if a test is negative and symptoms persist another test might be needed a few days later, particularly for those who use at-home test kits.

"So if someone is having symptoms and they get a negative test, one, it depends on the severity right? If you're having severe symptoms we don't want you to just do a home test either," Dr. Nimmi Rajagopal, the associate chair of the Department of Family and Community Medicine for Cook County Health, told NBC 5 during the omicron surge late last year. "We want you to call your doctor's office and make sure that they have an opinion here because there are of course other things like the flu that are out there that can mimic symptoms or have similar symptoms. But if you're having symptoms and they're kind of mild and lingering and you use the [at-home] test and it's negative, we want you to take the precautions and then retest in three to five days. And that's why most of these kits actually come with two tests."

"A person with COVID-19 is considered infectious starting two days before they develop symptoms, or two days before the date of their positive test if they do not have symptoms," according to the CDC.

Regardless of symptoms, those who test positive are advised to take specific precautions for at least 10 days.

"Lets say somebody is diagnosed with COVID and they are in a setting during a time that they might be infectious, we know that with COVID, for the first five days you need to be isolated because you can definitely be spreading COVID at that point," Chicago Department of Public Health Commissioner Dr. Allison Arwady said during a Facebook Live Tuesday. "And then you need to be out in day six-10 in that mask."

With high levels of tree pollen wafting through the air and COVID variants lingering around, it can be difficult to identify the reason behind the runny nose and fatigue. 

Before self-diagnosing, health officials have said the best way to identify the ailment is through testing, especially given some symptoms overlap between the coronavirus and seasonal allergies.

"Even if it's a sore throat, no matter what it is," Arwady said in a Facebook live last month. "I've told my own staff this, it's what I do myself... if you are sick, even a little bit sick, stay home. More true than ever right now because sick, even a little bit sick, until proven otherwise with a test - that's COVID. That's how we treat it, that's how you should treat it."

First, you'll need to know the difference between whether you must quarantine or isolate. Those who believe they have been in contact with someone who has COVID and are unvaccinated should quarantine. Those who test positive, regardless of vaccination status, must isolate, according to the CDC.

Close contact is defined by the CDC and the Illinois Department of Public Health as "someone who was less than 6 feet away from an infected person for a cumulative total of 15 minutes or more over a 24-hour period."

If you come into close contact with someone with COVID-19, you should quarantine if you are not up-to-date on COVID-19 vaccines or are unvaccinated. For these individuals, the CDC and IDPH recommend you:

Those who are close contacts of someone with COVID but are up-to-date on their vaccinations or have had a confirmed case of COVID-19 within the last 90 days do not need to quarantine, but the CDC does recommend they wear a well-fitting mask around others for 10 days after their most recent exposure and get tested after at least five days.

According to the CDC, people who are positive for COVID should stay home until it's safe for them to be around others, including even other members of their home.

Health officials recommend a "sick room" or area for those who are infected and a separate bathroom, if possible.

But isolation may not just be for those who test positive. The CDC also recommends those who have symptoms of COVID-19 and are awaiting test results or have not yet been tested isolate, "even if they do not know if they have been in close contact with someone with COVID-19."

How do you end isolation?

So how do you calculate your isolation period?

According to the CDC, "day 0 is your first day of symptoms." That means that Day 1 is the first full day after your symptoms developed.

For those who test positive for COVID but have no symptoms, day 0 is the day of the positive test. Those who develop symptoms after testing positive must start their calculations over, however, with day 0 then becoming the first day of symptoms.

Under the CDC guidance, those in isolation should:

While testing out of isolation is not required, the CDC says those who choose to should use an antigen test and not a PCR test. These can be taken toward the end of the isolation period.

"Collect the test sample only if you are fever-free for 24 hours without the use of fever-reducing medication and your other symptoms have improved," the CDC states. "If your test result is positive, you should continue to isolate until day 10. If your test result is negative, you can end isolation, but continue to wear a well-fitting mask around others at home and in public until day 10."

After quarantining for the appropriate amount of time, those who were exposed should continue to watch for symptoms until at least 10 days after their exposure. If symptoms develop, they should isolate immediately and get tested.

After ending isolation, the CDC recommends individuals continue wearing a mask through day 10, or continue isolating for a full 10 days if masking isn't an option. They also urged these individual to avoid anyone with a weakened immune system or those at higher risk of infection for the full 10 days.

The CDC urges those who have or may have COVID-19 to watch for emergency warning signs and seek medical care immediately if they experience symptoms including:

"This list is not all possible symptoms," the CDC states. "Please call your medical provider for any other symptoms that are severe or concerning to you."

You can also notify the operator that you believe you or someone you are caring for has COVID.

Those who test positive using an at-home test are asked to follow the latest CDC guidelines and communicate the results to their healthcare provider.

Arwady has said that that process is not likely happening for every test, however.

"All of those negatives realistically are not being reported," Arwady said. "We're not counting, you know, it's a fiction that we've ever counted every COVID test."

The at-home results are part of the reason Illinois' health department changed the COVID metrics it tests.

With the state no longer reporting COVID case and test positivity, health officials said the reason is in part due to incomplete data due to at-home tests.

The department said the change, in part led by the fact that national testing data does not often reflect results from at-home tests, means that labs will no longer be required to report negative rapid antigen test results, though they will still need to show negative PCR and nucleic acid amplification test results.