It could have already passed through all of those communities basically unnoticed, and/or confused with other ILIs. There's no way to rule out that possibility,

It could have already passed through all of those communities basically unnoticed, and/or confused with other ILIs. There's no way to rule out that possibility, and when you consider how rare cardiovascular diseases (the most common comorbidity) are in those communities, you have to conclude that it's not vanishingly unlikely: https://minorityhealth.hhs.gov/omh/browse.aspx?lvl=4&lvlid=49 https://minorityhealth.hhs.gov/omh/browse.aspx?lvl=4&lvlid=4... Obviously mitigation efforts still play some part in limiting the spread, but I would not bet that all of those communities were able to suppress such a contagious disease before a big chunk of the population was exposed to it.