State health officials confirmed nine deaths and 18 fresh cases of swine flu in the state on Sunday. With this, the death count has increased to 478 while the number of cases has gone up to 5,035 which is the highest recorded in the last four years. Mumbai reported highest six deaths followed by Aurangabad (2) and Pune (1). The condition of 17 patients is currently critical and they have been put on ventilator. "These deaths occurred in the last two to three days but the local authorities could confirm the cause of death only on Sunday," said a state health official. Of the nine people who died of swine flu, four had other co-morbid condition. "The four victims had other associated illness, including asthma, diabetes, and hypertension, while one of the victims was pregnant," official said. The H1N1 infection frequency is being closely monitored by scientists at the Pune-based National Institute of Virology (NIV). "The rate of swine flu infection has come down. However, it is imperative to continue monitoring the genetic make up of the virus to understand its adaptability and evolutionary dynamics," said an official from NIV.