Researchers who study infectious diseases are accustomed to spring bringing warmer weather and an end to the flu season. Because of the new coronavirus outbreak (COVID-19), this year has been far from business as usual.”Last week was a challenge, and this week is going to be even more challenging,” Dr. Bryan Lewis, a professor at the Biocomplexity Institute, told AccuWeather.In the United States, confirmed coronavirus cases have more than tripled in the last week – to 52,000-plus as of Tuesday compared to 14,500 – and that total is roughly 14 times the number of confirmed cases from only two weeks ago when it was 3,770.COVID-19 has now spread to more than 169 countries or regions with more than 415,000 confirmed cases and at least 18,500 deaths. The Illinois National Guard operates a COVID-19 drive-thru test site for medical personnel and first responders at a closed vehicle emissions testing center Wednesday, March 25, 2020, in Chicago. (AP Photo/Charles Rex Arbogast) “This is a significant event that may continue to cause continued challenges for influenza forecasting into the fall,” said Lewis, whose team at the University of Virginia works in a research partnership with AccuWeather. “We are already altering these methods to try and forecast COVID-19, and because it will be tracked by the ILI surveillance system [influenza-like illness], the forecasts in the coming weeks will be capturing this activity.”The new coronavirus (COVID-19) outbreak has created a third spike in ILI activity across the U.S., as the Biocomplexity Institute team predicted, according to the Centers for Disease Control and Prevention (CDC).Visits to health care providers for ILI increased for the second straight week to 5.8 percent after it was 5.2 percent last week, according to the CDC. For comparison, the highest peak during all of last year’s difficult flu season was just 5.1 percent. “The season remains very active, registering another increase in activity nationally, with over half the states (35) reporting an increase in the most recent surveillance report,” this week’s Biocomplexity report notes. “Five states are currently registering a record high level (since 2010) and a large part of the country (36 states) are higher than they’ve ever been for this time of year. The season remains extremely active and should continue to be so for weeks to come.”This season is on track to be the longest above-baseline flu season in at least 20 years of CDC records; it’s the 18th straight week flu activity is above baseline normal (2.4 percent).ILI activity has had longer stretches just twice since 1999-2000, according to CDC records, and this season’s third spike is just starting to ascend. The other years were 2018-19 (20 weeks) and 2014-15 (19 weeks); this year is now tied with the flu pandemic season of 2009-10.CLICK HERE FOR THE FREE ACCUWEATHER APP”The staggering rate of growth [of COVID-19] in most of the states we are seeing last week – and I think will continue this week – is a result of long overdue testing finally coming online,” Lewis told AccuWeather. “Basically, there were probably 40,000 to 50,000 infections, if not more, circulating in the U.S. a week to 10 days ago, and we are just now starting to catch up.”Researchers believe the quarantining and social distancing efforts enacted throughout the U.S. should help reduce both ILI activity and COVID-19 transmission. Despite those efforts, researchers point out that the major interruptions to daily life could last for several months.”I think if anybody thinks we’ll be doing this for two weeks and then we’re done … I don’t think that’s going to work out. We’ll go right back where we started,” Madhav Marathe, a director and distinguished professor of the Biocomplexity Institute, told AccuWeather’s Bill Waddell. “I strongly believe that all the state governments in the U.S. should actively start building temporary medical facilities. I think it’s centrally important.”Flu season typically begins in October, peaks between December and February and lasts well into March, although activity can last as late as May. Flu viruses are more stable in cold air and the low humidity allows the virus particles to remain in the air, according to Peter Palese, who was the lead author on a key flu study in 2007.Keep checking back on AccuWeather.com and stay tuned to the AccuWeather Network on DirecTV, Frontier and Verizon Fios.