Coronavirus cases are rising in 22 of the 50 U.S. states, according to a Reuters analysis, a worrisome trend on a Labor Day holiday weekend traditionally filled with family gatherings and parties to mark the end of summer.

As little as three weeks ago, cases were increasing in only three states, Hawaii, Illinois and South Dakota, according to an analysis comparing cases for the two-week period of Aug. 8-22 with the past two weeks.

Most of the 22 states where cases are now rising are in the less-populated parts of the Midwest and South.

On a percentage basis, South Dakota had the biggest increase over the past two weeks at 126%, reporting over 3,700 new cases.

Health officials have linked some of the rise to hundreds of thousands of motorcyclists who descended on Sturgis, South Dakota, for an annual rally in August.

Cases are also rising rapidly in Iowa, with 13,600 new infections in the past two weeks, and North Dakota, with 3,600 new cases in the same period.

The increases are masked nationwide by decreasing new infections in the most populous states of California, Florida and Texas.

In California, cases fell by 39,000 over the past two weeks compared with the prior two weeks, compared to a 37,000-case increase in the 22 states in the same period, according to a Reuters analysis of state and county data.

While cases nationally have dropped from a peak in July, the United States is going into the Labor Day holiday weekend with an average of 44,000 new cases a day — double the number ahead of the May 23-25 Memorial Day weekend.

Many health experts partly blame the July spike on social gatherings held around Memorial Day.

At the same time, the United States continues to average about 1,000 new deaths from Covid-19 each day, with the total number of lives lost approaching 190,000 — the highest death toll in the world.

Also contributing to the spike in U.S. cases is the re-opening of schools and colleges in many areas and the large gatherings taking place despite the warnings of health experts, ranging from protests against racial injustice to rallies in support of President Donald Trump.

The government’s top infectious disease expert, Dr. Anthony Fauci, has said that it is crucial that the outbreak be contained before the cold weather sets in, when influenza cases are likely to spike alongside Covid-19 and more people begin to move indoors, increasing the risk of contagion.