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Michigan reaches critical indicator in fight against COVID-19


Fewer than 3% of COVID-19 diagnostic tests in Michigan have been positive in the last seven days, bringing the state to a positivity low not seen in a year.

About 2.53% of tests have come back positive in a seven-day period ending Sunday, which might be a sign the spread of COVID-19 is slowing. 

Experts note a positivity rate of 3% is a benchmark to show spread is limited. The state spent most of the winter well above that rate, hovering closer to 10%. 

The state peaked at about 60% daily positivity in mid-March of last year, when testing was extremely limited in the early days of the pandemic. This year, the highest daily positivity rate was just shy of 18% in early April when the state led the country in cases per population.

"Three percent is ... definitely a good sign," said Josh Petrie, research assistant professor of epidemiology at the University of Michigan. "We're in the lower threshold. It's about as good as you can be in percent positivity."

The positivity rate is calculated by dividing the positive number of COVID tests by the total tests given. It serves as a "rough indicator of community-based transmission," said Nigel Paneth, distinguished professor emeritus of epidemiology, biostatistics and pediatrics at Michigan State University.

But the positivity rate isn't the only factor that determines whether spread is under control. Paneth recommended people look at COVID-19 statistics holistically. That means also looking at numbers like the vaccination rate in the state and how many people are becoming ill.

About 60.4% of Michigan adults have gotten at least one dose of a COVID-19 vaccine as of June 7, data from the Centers for Disease Control and Prevention shows. Experts want to get that number up to at least 70% to help slow the spread even further.

About 43.1% of the entire state population is fully vaccinated.

"We need to look at all of the numbers and put a whole story together," Paneth said. "We can't just use one indicator and say, 'ah, as long as that indicator's OK, we can do things.'"

Both cases and testing positivity in the state have declined for the last seven weeks.

Michigan is out of the nation's top 10 at 22 cases per 100,000 — a decrease from a high of 519 cases per capita earlier in April. The Virgin Islands is leading at 134 cases per 100,000 people, outpacing Wyoming at 74 cases per 100,000 people, according to the CDC.

Grand Rapids, Kalamazoo, Saginaw, Jackson and Detroit are experiencing the fastest growth in COVID-19 cases.

Those ages 10-19 have the highest case rates in the state, followed by 20-29, then 30-39. Since April, case rates have decreased more than 50% for those between the ages of 50 and 79.

As of Friday, 846 people were hospitalized with COVID-19 with 252 in an intensive care unit and 157 other patients on ventilators. That's a 79% drop from April 19 when hospitalizations peaked with 4,158 patients.

Michigan has had 890,764 confirmed cases and 19,376 deaths since the virus was first detected in March 2020, according to the state Department of Health and Human Services.

Some parts of the state have fared better than others in the past seven days of testing, numbers reported Monday show. In Wayne, Oakland and Macomb counties, the state's most populated, the positivity rate in the past seven days is below 3%. In Detroit, which is counted separately, the positivity rate in the last seven days is 3.37%.

Most of the counties with a rate above 3% are ones where only a few tests are being given. St. Joseph County, which has a positivity rate of 8.28% over the seven days from May 31 to June 6, reported only 101 tests on its busiest day.

Oscoda County had a positivity rate of 17.56% in the same week for 80 tests total. Wayne County, in comparison, regularly reports the results of more than 1,500 tests, sometimes closer to 3,000 in a day. Oscoda County had a positivity rate of 17.56% in the same week.

Part of the reason for the decline in positivity rate is that more tests are available. In the early days of the pandemic, people would sometimes not get tested because tests were hard to come by. Increased access in many places means that people can get tested for any respiratory illness, including allergies and colds

"We had very little in terms of coughs and cold this past winter. That seems to have been a consequence of the masking for COVID," Paneth said. "Now that Michigan is dropping the masking, we have more coughs and colds. You can see how that would lead to more people going for testing."

From May 31 to June 6 of this year, the state reported 130,060 tests, up about 27.1% from a year ago for the same dates. The positivity rate for that time frame in 2020 was about 3.06%.

Petrie said that when positivity rates fall, it helps health departments return to one of their most important jobs: contact tracing.

With fewer people getting sick, it's easier for health officials to figure out where localized outbreaks are happening and stop them from getting worse, Petrie said. That helps to stop the spread further, which brings positivity rates even lower.

There is also a much bigger factor at play. Petrie pointed to vaccines as the one tool that has brought the positivity number down from earlier peaks.

Many of the places with the highest vaccination rate also have the lowest positivity rate. Leelanau County, for example, has vaccinated 73.9% of people 12 and older, the highest percentage in the state according to CDC data. It hasn't had any positive tests since May 25.

Getting vaccinated is the one thing the average Michiganian can do to help get their life back to what is was before the pandemic, Petrie said. It's likely that there will be COVID outbreaks seasonally, much like we have with the flu, he said. But if the majority of the population is vaccinated, those outbreaks will be limited in scope and won't overwhelm hospitals. 

It appears vaccines are also helping to protect people against COVID variants, which are strains of the virus that have mutated over time. Some of those variants have been found to be potentially more contagious.

As of May 28, Michigan has 11,569 confirmed cases of COVID-19 variants — the majority, or 10,957 cases, being B.1.1.7.

The fact that Michigan is able to maintain a lower positivity rate even though some of the variants have been found is "just another encouraging sign" of how well the vaccines work, Petrie said.

"The positivity rate is just one part of it, but if you look at these metrics across the board, they're at these lower thresholds," he said. "I think particularly if people are vaccinated, they can really feel comfortable with beginning to get back to normal."

hharding@detroitnews.com

Twitter: @Hayley__Harding

Staff Writer Sarah Rahal contributed.