It may already be spring, but viral illness season is not over yet.
The flu and the COVID-19including a new variant called BA.3.2, ―dubbed cicada (cicada, in Spanish)― continue to circulate, along with other respiratory diseases and an uncomfortable virus stomach that is making many sick.
The symptoms of most viruses are so similar — runny nose, cough, muscle aches, fever — that doctors have a hard time diagnosing the conditions.
Influenza A hit very hard in the United States at the end of last year. When it peaked in January, “we started seeing more of these other viruses,” said Marlene Wolfe, an associate professor of environmental health at Emory University. “Every year we think of fall, winter and spring as the season for respiratory diseases,” he added, “but the reality is that there are different viruses that appear throughout that season.”
Arkansas, North Dakota, Vermont and Wyoming continue to see moderate numbers of respiratory illnesses, while infections are low in the rest of the country, according to the latest data from the Centers for Disease Control and Prevention (CDC).
RSV respiratory syncytial virus cases remain high in some states, including Michigan, Nebraska, Nevada, South Dakota, Tennessee, West Virginia and Vermont.
How to distinguish between diseases?
“Unfortunately, there’s really no distinguishing feature between these respiratory diseases,” said Dr. Greeta Sood, an epidemiologist at Johns Hopkins Bayview Medical Center in Baltimore.
The symptoms of COVID-19 are no longer characterized by loss of taste and smell, as was the case in the early years of the pandemic, he noted.
“We also can’t predict, like we used to, what a person has based on what’s circulating. It could be COVID-19, it could be the flu, and now long-term RSV has been added to the mix,” Sood said.
Right now, local wastewater data, which measures the prevalence of different viruses in a community, could offer clues about what ailment a sick person might have.
“The situation is relatively calm for these diseases compared to other years, but where you live can make one or the other more likely,” said Jennifer Nuzzo, director of the Pandemic Center at the Brown University School of Public Health.
Wolfe agreed that it is important to understand what viruses are circulating in each community, as this can vary greatly from state to state.
“The dynamics of when and where we see more cases differ from virus to virus, so it’s important to know what’s happening in your community. Right now we still have several respiratory viruses that typically circulate in early spring,” he explained.
New variant of COVID-19
Almost no one wears face masks anymore. Relatively few people received the new COVID-19 vaccines this winter, in part because of confusion over who was eligible.
The CDC has reported that the highly mutated COVID variant called BA.3.2 has been detected in wastewater and nasal swabs in 25 states. The spike proteins of this variant have mutations that experts fear could allow it to evade immunity derived from previous infections or booster doses.
“This variant is very different from an immunological point of view compared to the previous ones, and when that happens, there is always the risk that, because we have less immunity against this pathogen, it could cause an increase in cases,” Sood said.
Only about 0.55% of COVID-19 viruses sampled in the United States in mid-March were the BA.3.2 variant, the most recent CDC data showed. Coronavirus cases did not spike in Europe after the first detected case of BA.3.2 last April, the agency reported. Right now, CDC data indicates that COVID cases, although at low levels, are increasing in Florida and Massachusetts, while decreasing in the rest of the country.
In the United States, “overall, it does not appear that COVID-19 cases are increasing dramatically,” Sood added, adding that it is too early to know whether BA.3.2 will cause an increase in cases. “There have been several variants that have similarly been very different immunologically, and we haven’t seen a wave.”
CDC data indicates that the situation of COVID-19 cases varies across the country. Numbers are high or moderate in some areas of the South, the Midwest, the Washington DC area and Appalachia, and low in the West and Southeast. Data from WastewaterSCAN, a public health initiative that collects surveillance information through wastewater, indicated an uptick in COVID-19 cases.
“COVID has not yet entered into a predictable pattern,” Nuzzo said, adding that a slight increase in coronavirus cases in certain states “is not something to be alarmed about. We do not see any concerning trends for COVID-19 at this time.”
Still, people at high risk of complications should consider getting a booster dose about every six months, he said.
“I’ve timed COVID booster doses with travel, when I really don’t want to get the virus, or when local numbers are rising. People need to take into account different factors in their lives, based on local trends and other circumstances,” Nuzzo said.
The flu
The early surge in flu cases this season was driven by a mutated strain of influenza A, or H3N2, called subclade K. Cases spiked between Thanksgiving and early January, and some experts feared the United States would repeat last year’s deadly flu season, which killed nearly 800 children and teenagers.
“It didn’t turn out to be as bad as last year’s flu season, which isn’t saying much since last year was the worst on record,” Nuzzo added. “Last year more children died from the flu than any other year, including 2009 when we had a flu pandemic.”
The CDC has so far recorded 115 childhood flu deaths this season, following two consecutive record-breaking years. The 2023-24 flu season claimed the lives of 199 children and adolescents, equaling the previous record of 2019-20. However, infections remain deadly: A California teenager died in early March from the flu, one of 14 child deaths recorded that week.
Influenza A cases began to decline in January and continue to decline nationwide, although the strain continues to cause infections and accounts for the majority of cases. Influenza B cases are increasing in Washington and North Dakota, but decreasing nationally, according to CDC data. Those from WastewaterSCAN showed the opposite: that influenza B cases remain high nationwide and are increasing.
“Influenza B continues to show up in wastewater quite regularly,” added Wolfe, who is also director of the WastewaterSCAN program.
Sood said there is still time to get a flu vaccine, especially for people who received their last vaccine in early fall.
“If you’re going to travel and want to get vaccinated, it’s not too late, but we’re closer to the end of the season than the beginning,” Sood said.
Respiratory syncytial virus (RSV)
Respiratory syncytial virus, or RSV, can cause an annoying cough along with a runny nose and fever. Although it can be difficult to distinguish from the common cold, RSV can be dangerous to children and babies.
“This season, RSV has stabilized, but we are still detecting fairly high levels in the wastewater,” Wolfe said.
CDC wastewater data showed that RSV is generally circulating at moderate levels nationwide, but the virus remains at high or very high levels in Hawaii, Iowa, Michigan, Minnesota, Nebraska, Nevada, New Hampshire, South Dakota, and Wyoming. Cases continue to rise in North Dakota.
“RSV usually appears early in the season, as it did, but what is unusual right now is that it is not declining as much as one would expect,” Sood said. “Some states still recommend that babies born at this time receive RSV antibodies; normally, the RSV season would be considered over by now.”
Human metapneumovirus (HMPV)
Human metapneumovirus, or HMPV, is a virus related to RSV that causes symptoms similar to those of the common cold. According to WastewaterSCAN, HMPV is circulating at high levels across the country, although this was to be expected, Wolfe added.
“HMPV is fairly consistent in the wastewater data and tends to peak in mid-April,” he said.
Norovirus, vomiting and diarrhea disease
Among the viruses that are spreading widely at the moment, you will know if what you have is norovirus. Although it is sometimes called the “stomach flu,” it is a gastrointestinal virus, not a respiratory one. This nasty and extremely contagious virus has been circulating at high levels for months and continues to wreak havoc. In a recent outbreak, more than 150 people, including passengers and crew, aboard a Princess cruise ship fell ill with norovirus, according to the CDC.
People with norovirus suddenly experience vomiting, diarrhea and nausea, which usually lasts a couple of days, which has earned it the name “two bucket disease.”
WastewaterSCAN noted that norovirus loads remain high across the country, but are not increasing. Last cold and flu season, the United States experienced an abnormally high number of norovirus cases, Wolfe said. So far, the CDC has recorded less than half as many norovirus cases this season compared to last.
“What we’re seeing this year looks a lot like the pattern we saw before,” he said. “We saw norovirus peak at the end of February and cases seem to be leveling off. It’s good to see it’s not as bad as it was last year.”
