CVS Health is being sued for allegedly revealing the HIV status of 6,000 patients in Ohio.
The complaint was filed in federal court on March 21st.
The patients in question were part of Ohio's HIV drug assistance program.
The lawsuit claims that CVS mailed letters last year where patients' HIV status could be seen through the glassine window.
Fiserv, the company that CVS hired to mail the letters, is also named in the lawsuit.
In a statement to CNN, CVS Health said the envelope window was intended to show a reference code for the assistance program and not the recipient's health status.
"CVS Health places the highest priority on protecting the privacy of those we serve, and we take our responsibility to safeguard confidential information very seriously," the statement said.
"As soon as we learned of this incident, we immediately took steps to eliminate the reference code to the plan name in any future mailings."
A representative for Fiserv told CNN the company does not comment on pending litigation.
The plaintiffs are seeking class-action status and a jury trial.
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Lawsuit: CVS unintentionally revealed HIV status of 6,000 patients
U.S. & WORLD