What the research found
A 2025 study in PNAS Nexus analyzed 12 years of archived website data from 1,201 large US hospitals, tracking the use of tracking pixels (invisible embedded snippets that send visitor data to outside companies) and comparing pixel use against reported data breaches at each hospital. Third-party pixel use showed up on 66% of hospital websites sampled. Hospitals using third-party pixels had a data breach probability 1.4 percentage points higher than hospitals that didn’t, a 46% relative increase over the 3% baseline breach rate in the sample. First-party pixels, which keep data inside the hospital’s own systems rather than sending it to an outside vendor, showed no connection to breach risk. The difference sat in data leaving the building.
The paper points to two real cases behind these numbers. Community Health Network disclosed a breach affecting about 1.5 million patients in 2023, traced to tracking pixels sending data to third parties. Advocate Aurora Health reported a breach covering 3 million patients in 2022, tied to the same mechanism: pixels sending information to Meta.
Why the same small piece of code shows up everywhere
A tracking pixel works the same way whether it’s embedded in a marketing email you opened this morning or sitting on a hospital appointment page: a tiny, invisible image that loads from a server the moment you view the content, confirming you opened it and often what page you were on when you did. In an email, that mostly confirms you’re a reachable inbox. On a hospital website, the same mechanism can transmit far more sensitive signals: an IP address tied to a specific appointment request, browsing patterns tied to medical conditions people were researching. The technology doesn’t distinguish. The stakes attached to what it’s tracking do.
Regulators have taken notice in healthcare. US Health and Human Services issued guidance in December 2022 stating that IP addresses linked to hospital webpages could count as protected health information, and HHS and the FTC sent warning letters to 130 healthcare providers in 2023 about tracking pixel risk.
The practical takeaway
You can’t audit which hospital or health system uses third-party pixels on your own, but you can limit what you expose regardless of the site. Browser extensions that block third-party trackers cut off a meaningful share of this exposure without any effort on your part after setup. For anything sensitive (a specific diagnosis, a mental health inquiry), avoid researching it through a search bar or a portal you’re logged into on a device or browser where you’d rather that activity not be linked back to your identity.
This research establishes a strong statistical association between third-party pixel use and breach risk, with the authors running several checks to rule out reverse causation. It doesn’t prove each pixel-related exposure results in a reportable breach, and hospitals vary in which vendors they use and how those vendors handle the data they receive.
Reference
Atasoy, H., McDonough, R., Zhang, G. M. “Beyond the click: Pixel tracking technologies and patient data security in hospitals.” PNAS Nexus, 2025. https://doi.org/10.1093/pnasnexus/pgaf360
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