Teikyo University Hospital said Friday that since late last year 27 out of 46 patients infected with an antibiotic-resistant bacterium called Acinetobacter have died, including nine whose deaths are possibly attributable to the superbug that the hospital did not report until Thursday.

The first death occurred last October, said the hospital in Itabashi Ward, Tokyo. It launched an in-house investigation panel this July but did not make an announcement.

Acinetobacter bacteria are microbes found in many parts of the environment, including sewage, soil and water. They are resistant to most antibiotics, but certain cephem antibiotics are effective in treating Acinetobacter infections, according to the hospital.