Background: Healthcare-associated infections (HAI) are the most frequent adverse event in health-care delivery worldwide. Antibiotic resistance threatens the effective prevention and treatment of an ever-increasing range of HAI caused by bacteria. There is an urgent need to investigate alterative preventive and treatment options while there are still a few antibiotics left. Bacteriophage (phage) therapy, the use of viruses that infect bacteria as antimicrobials, has been championed as a promising alternative to antibiotics. Methods & Materials: Commercial bacteriophage cocktail targeting Klebsiella pneumoniae was orally given over 5 days to patients hospitalized in the neonatal intensive care unit in Saint-Petersburg, Russia. Results: In July 2013 the incidence of nosocomial infections caused by K. pneumoniae in the neonatal ICU began to increase. The outbreak started with two cases of pneumonia caused by K. pneumoniae. 4 cases of nosocomial infections were identified in July. The number of cases of K. pneumoniae infection increased to 11 cases in August. Totally, HAI caused by K. pneumonia were occurred in 15 patients, the rate was 19.0% (95% CI = 11,0-29,4) during the outbreak period. Common measures to control the outbreak had been unsuccessful. After application of the phage cocktail among newborns, the rate of nosocomial K. pneumoniae infections decreased to zero and remained at this level for more than a month of surveillance in the ICU. Conclusion: Presented results clearly demonstrate high efficiency of bacteriophages. Phages have several features that make them potentially attractive antibacterial agents. Bacteriopahges are highly specific and very effective in destroying targeted bacteria, safe and rapidly modifiable to combat the emergence of newly arising bacterial threats.