The court hears that Lucy Letby was a "constantly bad" presence on the neonatal ward.
Between June 2015 and June 2016, Nurse is accused of killing seven babies and trying to kill ten more.
A court heard that a nurse killed seven babies and tried to poison 10 others on a hospital neonatal unit, where she was a "constantly evil presence."
A jury was told that Lucy Letby, who was 32 years old, killed babies by giving them insulin, air, or milk during night shifts when she knew their parents would not be there.
One of the babies was only 24 hours old when Letby allegedly injected him with air, killing him just 90 minutes after she started working. It is said that the nurse tried to kill his twin sister the next day.
The court heard that Letby, who was trained to care for the sickest babies, took a "unusual interest" in the parents of some of her 17 alleged victims and in some cases tracked them on Facebook.
Jurors were told that she was the only "common denominator" between the deaths of seven babies and the "catastrophic" collapses of 10 others at the Countess of Chester hospital between June 2015 and June 2016. The eight women and four men on the jury were told that she tried to kill some babies more than once, and in one case, three times.
The Manchester crown court heard that most of the 17 babies were born too early and were getting care in the intensive care unit or high-dependency unit when they were attacked by Letby.
The prosecutor, Nick Johnson KC, told the jury, "We say that the deaths and collapses of the 17 children named in the indictment were not normal tragedies. We say that all of these bad things happened because of the woman in the dock, who was always there when things went wrong for these children.
Letby, who has pleaded not guilty to killing seven babies and trying to kill 15 others, sat in the glass-enclosed dock of the court as the prosecution explained its case.
Some of her alleged victims' families were sitting in the audience a few meters to the right of the defendant. Letby's parents, John, 76, and Susan, 62, were sitting on the other side of the public gallery.
Johnson told the jury that the neonatal unit at the Countess of Chester was like any other in the country because it cared for sick or premature babies. But, he said, "a poisoner was at work" at this unit.
It is said that the babies were sometimes given insulin through a feeding bag and sometimes given air through a tube into their bloodstream.
The prosecution also says that babies were sometimes given too much milk or air through a tube into their stomachs. Johnson said that this would have been "catastrophic" for the babies.
He also said, "So, these babies were attacked in different ways, but Lucy Letby was always there when they were killed or fell apart in a terrible way."
Johnson said that since June 2015, when Letby is said to have killed or tried to kill babies, there has been a "significant rise" in the number of babies who died or had "serious catastrophic collapses."
Consultants saw that babies who were dying got worse out of the blue and that babies who collapsed seriously could not be saved.
Consultants noticed that all of the deaths and collapses had one thing in common: one of the neonatal nurses, Lucy Letby, was there. This led the police to look into the deaths and collapses.
The jury was shown a chart that showed Letby was the only nurse on duty at each of the 22 murders or attempted murders.
Johnson said that many of the babies who died or collapsed suddenly did so during Letby's night shifts, when their parents were not there. When Letby was moved to day shifts, he said, "The collapses and deaths moved to the day shift."
The jury heard that Letby gave insulin to two newborn boys two days after they were born to kill them. Both babies, only known as Baby F and Baby L, were born to different sets of twins. They lived, but their baby brothers also died because they were poisoned. Baby E was the one who died.
Baby F and Baby L were first thought to have been poisoned by something that happened naturally, Johnson said. "It just never occurred to the doctors or anyone else in that hospital that someone in the neonatal unit would have given them insulin," he said.
He said, "No one would think that someone was trying to kill babies in the neonatal unit of a hospital."
The trial goes on.