[NOTE: Part I can be found here.]
Flu (otherwise known as influenza) has been around far longer than COVID. Flu comes every year and it kills a lot of people.
So one might think that we know a great deal about flu; for example, that the number of flu deaths per season would be known if not precisely, then at least fairly well, because everyone who has a very serious case would be tested for it. But actually, flu deaths are always estimated, and there are good reasons for that:
First, states are not required to report individual flu illnesses or deaths among people older than 18 years of age to CDC. Second, influenza is infrequently listed on death certificates of people who die from flu-related complications. Third, many flu-related deaths occur one or two weeks after a person’s initial infection, either because the person may develop a secondary bacterial co-infection (such as bacterial pneumonia) or because influenza can aggravate an existing chronic illness (such as congestive heart failure or chronic obstructive pulmonary disease). Also, most people who die from flu-related complications are not tested for flu, or they seek medical care later in their illness when influenza can no longer be detected from respiratory samples. Sensitive influenza tests are only likely to detect influenza if performed within a week after onset of illness. In addition, some commonly used tests to diagnose influenza in clinical settings are not highly sensitive and can provide false negative results (i.e. they misdiagnose flu illness as not being flu.) For these reasons, many flu-related deaths may not be recorded on death certificates. These are some of the reasons that CDC and other public health agencies in the United States and other countries use statistical and mathematical models to estimate the annual number of flu-related deaths.
Flu deaths in children are slightly different though because these are nationally notifiable, which means that individual flu deaths must be reported to the Centers for Disease Control and Prevention. States report flu-related child deaths in the United States through the Influenza Associated Pediatric Mortality Surveillance System. However, even deaths in children may be underreported, for many of the same reasons listed above.
You may have noticed that there are some similar problems with COVID reporting, in particular the aggravation of existing chronic illnesses muddying the waters of cause of death.
All flus are far from equal in their lethality or their symptoms, as I wrote in Part I. But flus tend to have certain basics, and COVID-19 has some resemblances to these basics in terms of symptoms, especially in mild cases – and similarities in the manner in which people die and also the co-morbidities that often help lead to their deaths.
There is very real complexity and difficulty in trying to design a system that can tell us how many flu deaths we have. This isn’t an issue I’d ever thought about prior to the COVID-19 pandemic, and I would guess most of you hadn’t, either. However, I’ve thought about it a lot ever since COVID became a big big deal, because it’s clear that ascribing a death to COVID isn’t a simple matter either. The criteria can vary a great deal, and it’s also tempting to compare the COVID death rate to the flu death rate and try to draw conclusions. And yet both of those rates are hard to pin down.
I also have thought about this topic for personal reasons. Several people with whom I was very close have died (or in the case of one, nearly died) in ways similar to those reported with COVID-19, although their deaths were several years ago.
I’ll tell you the story of one of these friends who died. She was in her mid-60s and had a pre-existing condition but had been doing pretty well for years. Then she got what seemed like a mild flu.
I don’t think she was ever tested for flu; at least, not that I know about. She had some typical flu symptoms but nothing at all major, and was functioning quite well. The suddenly one afternoon, she became confused and was having trouble breathing. He husband immediately took her to the ER that was about three minutes from their home.
She had walked to the car, but by the time they got there three minutes later, she was unable to walk out of the car. That was the detail that seemed particularly vicious and terrifying to me. She was taken (by wheelchair) into the ER, and immediately put into an induced coma and placed on a ventilator. Doctors had determined that she was suffering from ARDS, something I’d never heard of prior to that:
Causes may include sepsis, pancreatitis, trauma, pneumonia, and aspiration. The underlying mechanism involves diffuse injury to cells which form the barrier of the microscopic air sacs of the lungs, surfactant dysfunction, activation of the immune system, and dysfunction of the body’s regulation of blood clotting. In effect, ARDS impairs the lungs’ ability to exchange oxygen and carbon dioxide…
The primary treatment involves mechanical ventilation together with treatments directed at the underlying cause. Ventilation strategies include using low volumes and low pressures. If oxygenation remains insufficient, lung recruitment maneuvers and neuromuscular blockers may be used. If this is insufficient, extracorporeal membrane oxygenation (ECMO) may be an option. The syndrome is associated with a death rate between 35 and 50%.
Globally, ARDS affects more than 3 million people a year.
See that death rate? It’s brutal, absolutely brutal. You also might recognize the similarly of her story to that of the unfortunate COVID-19 victims who wind up on ventilators. The situation is even more puzzling with COVID-19, though, because it’s emerging that although COVID deaths may resemble those like hers, leading from flu to ARDS, COVID-19 might be different in important ways:
In a letter last week in the American Journal of Respiratory and Critical Care Medicine, researchers in Germany and Italy said their Covid-19 patients were unlike any others with acute respiratory distress. Their lungs are relatively elastic (“compliant”), a sign of health “in sharp contrast to expectations for severe ARDS.” Their low blood oxygen might result from things that ventilators don’t fix. Such patients need “the lowest possible [air pressure] and gentle ventilation,” they said, arguing against increasing the pressure even if blood oxygen levels remain low. “We need to be patient.”
I’m not a doctor and don’t have a deep understanding of this issue, but I’m aware that lower pressure is indicated in non-COVID ARDS as well:
Recent studies have shown that high tidal volumes can overstretch alveoli resulting in volutrauma (secondary lung injury). The ARDS Clinical Network, or ARDSNet, completed a clinical trial that showed improved mortality when people with ARDS were ventilated with a tidal volume of 6 ml/kg compared to the traditional 12 ml/kg. Low tidal volumes (Vt) may cause a permitted rise in blood carbon dioxide levels and collapse of alveoli because of their inherent tendency to increase shunting within the lung…
Low tidal volume ventilation was the primary independent variable associated with reduced mortality in the NIH-sponsored ARDSnet trial of tidal volume in ARDS.
More on ventilators and COVID:
To be “more nuanced about who we intubate,” as she suggests, starts with questioning the significance of oxygen saturation levels. Those levels often “look beyond awful,” said Scott Weingart, a critical care physician in New York and host of the “EMCrit” podcast. But many can speak in full sentences, don’t report shortness of breath, and have no signs of the heart or other organ abnormalities that hypoxia can cause.
“The patients in front of me are unlike any I’ve ever seen,” Kyle-Sidell told Medscape about those he cared for in a hard-hit Brooklyn hospital. “They looked a lot more like they had altitude sickness than pneumonia.”
We obviously have a lot to learn, and quickly. And not just about COVID, but about flu as well.
[NOTE: And now we also have people wondering whether some of the spike in flu deaths during late December and January may have been COVID-19 mislabeled as flu.]