Science Friday recently covered a recommendation from the CDC to use only sterile water for sinus rinsing. As a lifelong allergy sufferer with frequent sinus infections, rinsing out my sinuses with a neti pot has become a major component of my health and wellness routine, especially during the winter and spring cold and allergy seasons. So I was extremely alarmed when I heard, first through Science Friday, that the CDC was recommending that people only use sterile water for nasal rinsing.
The basic biology here is that there are species of amebae that live in fresh water called Acanthamoeba. If you drink them, they won’t make you sick, because the acid in your stomach will kill them. If you swim in fresh water where they live and are at high population densities, they can get into your eyes and cause keratitis, but that infection doesn’t spread to the rest of the body. They can also get into open wounds, or your nasal passages. There, the membranes in your sinuses are thin, and the amebae can move into your brain. The resulting infection is usually fatal in about five days. That’s terrible news! And now the CDC has published a study showing that people have died from this brain infection because they were rinsing their sinuses with tap water. Well, I’ve been rinsing my sinuses with tap water for years, so I found this news to be terrifying. I could be days, or even moments away from death by brain eating microbe right now! Yikes!
I should add that I am not a medical professional; don’t take anything that I’m writing as medical advice.
But I do have a PhD in biology, and I’ve spent a lot of time looking at data. With that in mind, let’s take a look at the data that the CDC are talking about, and that news outlets have been covering.
The CDC study was published in April 2024, and it documents ten patients who reported nasal rinsing before an Acanthamoeba infection was detected, between 1994 and 2022. Nine of those cases were in the last decade. Seven of the ten patients survived.
Right away, it’s important to stop here and understand what’s going on in this paper. The researchers are talking about a phenomenon – amoeba infection following nasal rinsing – that they can show happened ten times in a span of 29 years. For public health risks, this is an extremely uncommon phenomenon. For comparison’s sake, there are about 80,000 methicillin-resistant Staphylococcus aureus infections in the US each year, and those infections kill about 11,000 people each year. With this study from the CDC, they’re talking about less than one infection per year. Of those ten patients, three died from the infection.
Patients that the CDC found were between 32 and 80 years old, with a median age of 60. Further, the CDC study notes that all of these patients were immunocompromised, five with cancer, two with AIDS.
Again, I’m not a medical professional, but when I saw those numbers and descriptions of the patients, I felt much less worried. As a scientist, it’s inappropriate and irresponsible to make inferences beyond the data. Here, the reported data only provide information about immunocompromised patients who are relatively old – older than the median American at least. Talking about these data as indicative of a major health risk for young, healthy people doesn’t make sense.
The scientists who wrote the peer-reviewed research article stayed within the bounds of their data. But the ways news outlets that covered this story have been pretty irresponsible. Science Friday did mention, ambiguously, that the patients in the CDC study were all immunocompromised, but you’d have to read past the headline and pretty carefully to notice. I can’t speak to how you’ll interpret the data, but I know that once I saw the data, I stopped worrying about this for my own health.
Along those personal lines, I recently had my annual physical with my primary care physician. During our conversation, I mentioned that using my neti pot had really been helping me avoid and recover from sinus infections. He asked if I use sterile water, and I said no. Oh, you really need to use sterile water, that’s the FDA and CDC recommendation, he told me. Yes, I said, I know. He told me that there was a recent study from the CDC showing a link between amoeba infection and neti pot usage with tap water. Yes, I said, I know, but what’s interesting about that is that the patients with those infections in the CDC study were all immunocompromised, and mostly older people. Oh no no no, he said, that’s not the case, someone in Florida just died, young healthy people are getting sick from sinus rinsing with tap water.
Now, it’s true that someone just died in Florida in March, probably from sinus rinsing with tap water. That person contracted an infection with a different amoeba, Naegleria fowleri. Infections from this amoeba are slightly less rare, with about 29 cases in the US from 2012 to 2022. Even more recently, a 2-year-old in Nevada died from this same microbe. Certainly these deaths are concerning, but the frequency is still quite low. An article from 2023 recommends that people plug their noses when jumping into freshwater lakes to avoid these infections. That would probably help a little, but this is still an extremely rare phenomenon. It would be great to prevent these deaths. But let’s keep in mind that about 4,000 people die every year in the US from drowning. So, sure, let’s try to prevent these infections, and, if we really want to keep more people alive, let’s teach people how to swim (and not to go swimming while intoxicated).
There was something positive about the Science Friday coverage, however: lots of people think that tap water is sterile. It’s not, and as a biology teacher, it’s always interesting to me to find places where people have scientific misconceptions. These amebae are common in many bodies of freshwater. If there’s an interesting story about the death in Florida, it’s that the amoeba was present in the tap water so early in the season, likely due to warmer water temperatures linked to global climate change. So there’s plenty of interesting science to talk about in this story. It just doesn’t make sense to talk about it as a major public health risk.
Knowing all of this, am I going to start using sterile water for my neti pot? Probably not. To me, the risk is just too low to worry about. Also, using bottled sterile water, or boiling and then cooling water, sounds prohibitively annoying. But I am going to try harder this summer to teach my kids to swim.