• Superinfections are a common complication in which a secondary bacterial infection occurs on top of the primary viral infection.
• People who have prolonged stays in the intensive care unit (ICU), like those with COVID-19 who can be hospitalized for weeks, are prone to secondary infections.
• Early evidence suggests that about 50 percent of people who’ve died from COVID-19 also had a secondary bacterial or fungal infection.

COVID-19 has already killed over 473,000 people, but medical experts are learning more about how the disease can lead to death.

Superinfections — a common complication in which a secondary bacterial infection occurs on top of the primary viral infection — are also to blame.

Early evidence suggests that about 50 percent of people who’ve died from COVID-19 also had a secondary bacterial or fungal infection, some of which were resistant to antibiotics.

Health experts aren’t surprised that patients with COVID-19 are battling superinfections in the hospital.

Superinfections frequently coincide with other viral infections like the flu. In fact, high death rates observed during past flu pandemics, including the 1918 flu pandemic, have mainly been caused by secondary bacterial infections, many of which are caused by drug-resistant bacteria.

“What’s going on here is that half of COVID patients are getting untreatable antimicrobial-resistant infections, so our antibiotics, our antifungals just don’t work,” said Corrie Detweiler, PhD, a microbiologist at the University of Colorado, Boulder studying drug resistance in bacteria and possible treatments.

“The superinfection problem isn’t new at all,” added Detweiler. “It’s just that COVID is highlighting it.”

Why patients with COVID-19 are getting superinfections

People who have prolonged stays in the intensive care unit (ICU), like those with COVID-19 who can be hospitalized for weeks, are prone to secondary infections.

Dr. Matthew Grant, a Yale Medicine infectious disease specialist, says this is due to a couple of reasons.

First is a condition called ventilator-associated pneumonia, a lung infection that develops when harmful germs get into a person’s lungs via the part of the ventilator that goes through the throat.

“This is not unique to people with COVID in the sense that people who have other respiratory viral illnesses of (this part of the) respiratory tract are also prone to bacterial pneumonia as a superinfection,” Grant said.

Patients with COVID-19 are also vulnerable to a number of other infections, like a urinary tract infection or bloodstream infection, since they’re often hooked up to IVs and catheters that can bring outside bacteria into the body.

“Basically, being on a ventilator, being sedated so you’re not moving around much, having all these tubes going into places they’re not normally going into, you’re at dramatically higher rates of day-to-day risk (for infections),” Grant said.

Some health experts suspect that certain treatments used on patients with COVID-19 could increase their risk of getting a secondary infection, Grant says.

For example, steroids, which have been used on people with severe cases of COVID-19, have a known risk of bacterial infection, says Grant.

Another immunosuppressant drug called tocilizumab, which is being used on patients with COVID-19, is also linked to an increased risk for bacterial infections, according to Grant.

How secondary infections affect people severely ill with COVID-19

Hospitalized patients with severe cases of COVID-19 experience massive lung damage, making them more susceptible to harm from dangerous pathogens.

When a healthy person breathes in a pathogen — which happens all the time — their immune system kicks in and kills them right away, according to Detweiler.

“If you’re really sick, then your immune system isn’t that well able to kill these opportunistic pathogens that are everywhere — they’re in your house, they’re on the playground, they’re in hospitals,” Detweiler said.

The immune systems of the sickest patients with COVID-19 produce a cytokine storm — a condition in which the immune system overreacts and causes widespread inflammation in the body.

A secondary infection could make a cytokine storm even worse.

“The cytokine storm is going to be exacerbated from a secondary infection. You’re going to have more of an inflammatory response,” said Detweiler.

Our bodies can’t kill a pathogen without killing some of its own cells, Detweiler explains, but there is a balance that has to be met.

An overwhelming immune response can kill too many healthy cells and cause massive tissue damage.

The immune system can also get worn down and be less effective when it’s over-activated for an extended period of time, as it can be with severe COVID-19.

“You’re not getting the same kind of effect or downstream help from the immune system that you get when you rev it up in the short term,” Grant said.

Some pathogens are resistant to treatments 

Though some of these bacterial infections can be treated with a course of antibiotics, others are resistant to the antimicrobial treatments that doctors commonly use.

Grant says ICUs are already enriched with multidrug-resistant pathogens.

“After a week in the ICU, your normal flora in normal parts of your body oftentimes gets replaced with drug-resistant bacteria,” Grant said.

Doctors have already reported several different kinds of pathogens in patients with COVID-19 who have secondary infections, the most common of which is Acinetobacter baumannii (A baumannii).

A baumannii, which causes infections in the blood, urinary tract, and lungs, is one of the more antibiotic-resistant types of bacteria.

These germs are difficult, if not impossible, to treat.

“(For these types of infections) if you did get sick and we gave you those antibiotics or antifungals, they wouldn’t work,” Detweiler said.

Superinfections are part of a much bigger issue

Detweiler says people who work on microbes have predicted we’d see increasing resistance among certain pathogens that cause secondary infections.

Unfortunately, there hasn’t been enough of a push to develop new types of antibiotics that can fight antimicrobial-resistant pathogens.

Without a whole new class of antibiotics, doctors will be unable to save some people who are dying from secondary infections, whether it’s with COVID-19 or another illness like the flu.

“I see the COVID issue as just highlighting what is a growing and alarming situation — and it’s worldwide, it’s not just the U.S.,” Detweiler said.

The bottom line

Nearly half of patients who’ve died from COVID-19 had a secondary bacterial infection. Sometimes, these secondary infections are resistant to antibiotics and antifungals, making them difficult and potentially impossible to treat.

Patients hospitalized with severe COVID-19 are susceptible to superinfections that occasionally are resistant to the antimicrobial available. Superinfections aren’t just a problem with COVID-19, and the novel coronavirus has shed light on a bigger issue we’re facing with drug-resistant bacteria.

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