High prevalence of hypervirulent Klebsiella pneumoniae infection in the genetic background of elderly patients in two teaching hospitals in China Chao Liu,1 Jiaojiao Shi,2 Jun Guo3,4 1Department of Respiratory Medicine, Peking Union Medical College, Chinese Academy of Medical Sciences, China-Japan Friendship Hospital, Beijing, China; 2Department of Respiratory Medicine, Peking University Third Hospital, Peking University, Beijing, China; 3Department of Respiratory Medicine, Beijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua University, Beijing, China; 4Department of Geriatric Respiratory Medicine, Chinese PLA General Hospital, Beijing, China Purpose: Aerobactin is a critical factor for hypervirulent Klebsiella pneumoniae (hvKp) in genetic backgrounds, but data based on the genotype for the elderly is limited. Materials and methods: A retrospective study was conducted on elderly patients from June 2008 to July 2017 in 2 teaching hospitals. The clinical and microbiological data, including antimicrobial susceptibility testing, string test, extended-spectrum β-lactamase (ESBL) production, virulence gene, and multilocus sequence typing, of the hvKp group defined as aerobactin positive were compared with those of classic K. pneumoniae isolates. Results: A total of 45.7% of 202 K. pneumoniae isolates were hvKp.ST23, which were predominant in 2 hospitals, but they were not highly associated with hvKp in different hospitals. Hypermucoviscosity, K1, K2, magA, and rmpA/A2 genes were highly related to hvKp (P