Summer heat is doing little to slow the spread of COVID-19 in Fresno region
There had been hope in some quarters that the Central Valley’s hot summer weather would slow or even halt the spread of the novel coronavirus.
But in Valley counties and across the state, quite the opposite has happened. The number of people being tested for COVID-19 is up, so more cases are to be expected. But the positivity rate – the proportion of people whose test results are coming back positive for the infection – continues to climb.
“Some viruses, like the common cold and flu, spread more when the weather is colder,” authors with the Harvard Medical School wrote this spring, in the early stages of the pandemic’s spread in the U.S. “But it it still possible to become sick with these viruses during the summer months.”
At that time, they added, “we do not know whether the spread of COVID-19 will decrease when the weather warms up.”
In the central San Joaquin Valley, at least, the verdict may be in. The average number of new daily cases so far in July is at least double — and close to triple — the number of cases in the previous month in four of five Valley counties.
Only in Kings County, where June was marked by an outbreak among inmates and personnel at state prisons, has the average number of new cases per day fallen since June.
Look at Fresno region
Fresno County’s average number of new confirmed coronavirus infections reported each day in May was just under 40. In June, it was up to almost 108 cases per day. Through the first 20 days of July, the daily average for this month is almost 7 1/2 times higher than May, at 294 new cases per day.
While the cumulative case counts have been fewer in other neighboring counties, the proportions of the summer surge have been even more pronounced in some:
Madera County’s daily average of new cases in May was just 1.8, and 13.4 in June. This month, that has ballooned to 46.5 per day – almost 26 times higher than in May as the pace of confirmed infections has picked up.
Merced County’s average number of new cases was 5.4 per day in May and 24.5 in June. So far in July, it’s been more than 14 times higher than May, at more than 78 cases per day.
Tulare County, which had the highest number of cases in the Valley for several months, reported an average of more than 40 new cases per day in May, fueled by outbreaks in skilled nursing facilities. In June, that doubled to 80.7. This month, the daily average is more than 133 new cases per day, or about 3.3 times higher than May.
Kings County averaged 19.9 cases per day in May, and climbed to 54.7 in June. Between June and July, the average shrank to about 37.5 – less than June, but still more than 1.7 times higher than May.
The Harvard Gazette reported in April that researchers at the university studied a pair of viruses that are genetically similar to the one that causes COVID-19 to examine whether they were susceptible to hot weather, not unlike the common cold or flu viruses that tend to spread in the winter “cold and flu season.”
“In every scenario modeled, they found that warm weather did not halt transmission,” the Gazette reported. “That was because, in the case of the common cold, a large segment of the population typically gets sick and develops immunity by spring. With (COVID-19), however, enough of the population will likely remain vulnerable, allowing it to spread even if transmission is reduced in warmer months.”
A doctor at Ohio State University’s Wexner Medical Center noted earlier this year that other parts of the world with high temperatures and high humidity, including Latin America, were experiencing coronavirus outbreaks. “More people get infected by one person with COVID-19 than with influenza,” added Dr. Seuli Bose Brill, who wrote the May article. “For this reason, weather changes may not eliminate COVID-19 infections.”
Bose Brill noted that while exposure to sunlight can cause the virus to die more quickly on surfaces, the effect on summertime transmission was unclear, “especially as most transmissions normally happen between people breathing on one another, with surfaces playing a smaller role.”
This story was originally published July 22, 2020 at 6:00 AM.
