A 2014 study published by the New England Journal of Medicine estimated that 4.0% of inpatients in U.S. acute care hospitals acquired an infection during their stay in the hospital. This impacted about "648,000 inpatients with a total of approximately 721,800 such infections in 2011." The study determined these figures by studying patients who "were receiving antimicrobial agents" at 183 hospitals. As the paper details, "antimicrobial therapy is a sensitive proxy indicator for health care-associated infections (sensitivity, 95 to 100%)." Although comprehensive data is unavailable, the rate of hospital-acquired infections almost surely increased during the Covid-19 pandemic because the disease is highly contagious and because many hospitals used ineffective measures like masks while failing to deploy a powerful Covid-killing technology called ultraviolet air disinfection.