They are testing from age 13 and up spring athletes (HS and clubs) every seven days.
Here is the Michigan SOP for Covid Testing/Classification/Etc. Updated March 2021. Lots of circular arguments, but I'm not certain if it is much different for other states.
https://www.michigan.gov/documents/mdhhs/nCoV_SOP_TEAM_680994_7.pdf
Terrible formatting from the report, but I'm guessing that many PROBABLE cases are being called positive (just a cough will get you a clinical PROBABLE reading even without a test). Interesting to dig through if you like to
Case Classifications
Confirmed
•Meets confirmatory laboratory evidence.
Probable:
•Meets clinical criteria AND epidemiologic evidence with no confirmatory laboratory testing performed for COVID-19.
•Meets presumptive laboratory evidence.
•Meets vital records criteria with no confirmatory laboratory evidence for SARS-CoV-2. Suspect:
•Meets supportive laboratory evidence*** with no prior history of being a confirmed or probable case.***For suspect cases (positive serology only), jurisdictions may opt to place them in a registry for other epidemiological analyses or investigate to determine probable or confirmed status.
Clinical Criteria
In the absence of a more likely diagnosis:
•At least two of the following symptoms: fever (measured or subjective), chills, rigors, myalgia, headache, sore throat, nausea or vomiting, diarrhea, fatigue, congestion or runny nose OR
•Any one of the following symptoms: cough, shortness of breath, difficulty breathing, new olfactory disorder, new taste disorder OR
•Severe respiratory illness with at least one of the following: clinical or radiographic evidence of pneumonia, or acute respiratory distress syndrome (ARDS)Laboratory CriteriaConfirmatory laboratory evidence: •Detection of SARS-CoV-2 RNA in a clinical or autopsy specimen using a molecular amplification detection test
Presumptive laboratory evidence:
•Detection of SARS-CoV-2 by antigen test in a respiratory specimenSupportive laboratory evidence: •Detection of specific antibody in serum, plasma, or whole blood
•Detection of specific antigen by immunocytochemistry in an autopsy specimen
Epidemiologic Linkage
One or more of the following exposures in the prior 14 days:
•Close contact* with a confirmed or probable case of COVID-19 disease
•Member of a risk cohort as defined by public health authorities during an outbreak. *Close contact is generally defined as being within 6 feet for at least 15 minutes. However, it depends on the exposure level and setting; for example, in the setting of an aerosol-generating procedure in healthcare settings without proper PPE, this may be defined as any duration. Data are insufficient to precisely define the duration of exposure that constitutes prolonged exposure and thus a close contact.Exposure does not have to be consecutive minutes.