Illness onset refers to the date when a patient with a confirmed case actually started getting sick. The metric can offer a better trend gauge than number of new cases due to reporting delay, but has its own shortcomings because most, but not all, known cases are reported.
Up until the last full week in April, the number of COVID illnesses starting on any given day peaked on April 6 with 174 people reported first having symptoms. Since then, the peak has moved toward the tail of the graph, meaning more recent, and jumped higher — in addition to clustering with other high points. As of the last weekend in April, for the first time, this chart shows most cases ever in the past few days, on April 20 at 214, and the two next highest points in the last two weeks as well — a departure from previous trends. Both single day reports and averaging the number of illnesses weekly show variability without a steady downward trend.