Jason Robinson ran in a hat-trick as England outscored the Azzurri 7-0 on tries, with Iain Balshaw, Josh Lewsey, Paul Grayson and substitute back row forward Chris Jones - who celebrated his England debut with the final scoring act - also going over.
"England are an incredibly complete team, and I thought that Paul Grayson had an outstanding game at fly-half." Kirwan said.
"When one player goes out another player comes into the team and takes his chance. It was a fantastically disciplined performance by England and they demonstrated why they are world champions.
"When you play against England you cannot make silly mistakes. The scoreline was too heavy, and we will definitely have to improve."
England's emphatic success underlined their status as clear favourites to land a second succession RBS 6 Nations crown, and asked how anyone could stop them Kirwan replied: "Maybe with a bazooka!
"Teams that play against them will need to hang on to the ball and try to move it around, but the beauty of England, is that they have about four different game plans.
"If you can recycle the ball quickly against them and go wide then you can make a game of it, but if you make too many errors, then you will concede 50 points."
Italy now face a daunting trip to Paris next Saturday, where World Cup semi-finalists France await them, but with a home game still to come against Scotland next month the wooden spoon might be eluded.
"This weekend, there have been great performances by France, Wales and now England, but this is only the beginning of the tournament and we can definitely improve," Kirwan added.
"We need to cut down on our errors, but we are looking forward to going to Paris."