In the wake of the COVID-19 pandemic and amid a large wave of respiratory viruses, health officials in Colorado and Minnesota have documented an unusual spike in deadly and invasive infections from Streptococcus bacteria late last year, according to a study released this week by the Centers for Disease Control and Prevention.
The spike is yet another quirk of post-pandemic disease transmission, but one that points to a simple prevention strategy: flu shots.
The infections are invasive group A streptococci, or iSGA for short, which are caused by the same group of bacteria that cause relatively minor illnesses, such as strep throat and scarlet fever. But iSGA occurs when the bacteria spreads through the body and causes a serious infection, such as necrotizing fasciitis (flesh-eating disease), toxic shock syndrome, or sepsis. These conditions can occur quickly and be fatal.
Usually iGAS is rare. But following the pandemic disruptions, there have been unusual increases in several countries. In December, the World Health Organization noted that five countries in Europe had reported unusual increases in cases, along with a number of deaths. The list includes the UK, which recorded at least 285 deaths (29 in children aged 10 and under) in England during the 2022-2023 iGAS wave, according to the latest data. The other four European countries are France, Ireland, the Netherlands and Sweden.
The CDC also noted an unusually high and early increase in iGAS cases in children at the end of 2022. In the new study, local health officials report data from surveillance sites in the Denver metro area and of the State of Minnesota. Between October 1 and December 31, 2022, there were 34 cases of iGAS in children from the two surveillance sites, including two deaths. This is a jump from the pre-pandemic period, but not from the cases seen at the height of the pandemic, when the incidence was exceptionally low. During the same three-month period in the years before the pandemic (2016 to 2019), the average number of cases for the two sites totaled only 11 cases. But from 2020 to 2021, amid pandemic mitigation efforts, the average was just four cases. From 2016 to 2021, there have been five GAS deaths in total.
Officials found that the 2022 bump did not appear to be linked to an unusual strain of strep A or new drug resistance. But they pointed out that it coincided with waves of respiratory viruses, namely influenza and RSV (respiratory syncytial virus).
This is not surprising, since group A strep is known to piggyback on viral infections. Historically, researchers have linked group A strep to the spread of chickenpox. And vaccination against varicella has been shown to reduce rates of group A streptococcal infections in children. But the researchers noted that other viral infections can also pave the way for group A strep.
It is unclear why some viral infections are linked to group A streptococcus. As Ars has previously reported, researchers have speculated that it may involve factors such as overlapping disease cycle, similar transmission (eg, respiratory) and common age of victims. It is also possible that some viral infections use the same methods as streptococci to suppress human immune responses and trigger an infection. So, if a virus gets there first, it can make it easier for streptococcus to take hold. Such viral-bacterial binding has been observed elsewhere; before vaccination campaigns, waves of the measles virus were closely linked to increases in whooping cough caused by the bacteria Whooping cough Bordetella. Measles is known to largely dampen immune responses, leading to what some researchers describe as “immune amnesia.”
In the unusual increase in iSGA this season, health officials suggest that waves of influenza and RSV may have allowed the bacteria to spread and its disease potential. Case reporting shows a strong link between virus spread and iGAS cases in recent years, as well as last year. And previous studies have also shown that respiratory viruses and influenza, in particular, can increase the risk of iGAS. Of the 34 iGAS cases in 2022, 15 had positive test results for one or more viral infections during or before their iGAS case, including six for influenza, six for RSV and three for SARS-CoV- 2. (It’s unclear how many of the 34 children were tested for viral infections. Only positive results were reported.)
“The increased activity of respiratory viruses, associated with reduced exposure to (group A strep) and the associated development of protective immunity against common types (strep A) during the COVID-19 pandemic, may have predisposed the children to iGAS infection when pandemic restrictions were lifted,” the authors conclude. But the results suggest a possible prevention strategy. “Influenza vaccination may reduce the risk of iGAS, as has been shown for varicella vaccination,” they write.
Although an RSV vaccine is not yet available, several are in the pipeline.