Levels of the vomiting bug norovirus are now higher than in previous years, figures show.
New data from Public Health England (PHE) shows there have been 1,704 cases of norovirus in England confirmed by laboratory testing so far this season, which is 9% higher than the average for the same period over the last five years.
The figure is also 55% higher than the same period last year, although last winter saw unusually low levels of norovirus.
Overall, in the last two weeks of November, there were 14 outbreaks of norovirus in hospitals, all of which led to ward closures or the closure of bays.
In total this season, there have been 105 hospital outbreaks reported.
The number of laboratory reports of the bug rotavirus this season is 938, which is also 9% higher than the average for the same period from 2003 to 2013.
Julia Scott, chief executive of the College of Occupational Therapists, said: "The rise in norovirus infections highlighted in today's figures means that it is vital the NHS does everything it can to prevent unnecessary admissions to hospital and to ensure that patients can go home as soon as they are medically fit.
"Delayed discharges increase the chance that someone who could go home may contract norovirus and become sicker than they were on admission."
The norovirus figures come as new data from NHS England shows the health service continues to struggle as winter bites.
Just 89% of patients were dealt with in A&E within four hours in October, against a target of 95%. The total number of A&E attendances was up 4% compared with the same period last year.
Other targets were also missed, including for patients to start treatment led by a consultant within 18 weeks, and cancer patients to start their first treatment within 62 days of urgent GP referral.
Delayed discharges are also the highest on record. This is when patients are medically fit to leave hospital but are unable to do so because social care packages or other care is not in place in the community.
The proportion of calls abandoned by people seeking help from the 111 helpline has also risen to 2.4% of calls in October, up from 1.5% in September.
Ambulance trusts across England also continue to miss targets for responding to life-threatening calls.
More tests to diagnose conditions were performed, although the proportion of patients waiting six weeks or more for results has risen slightly.
Matthew Swindells, NHS England's national director of operations and information, said: "These figures suggest A&E attendances are increasing rather faster than the growth in the number of major "accidents" and medical "emergencies", putting great strain on A&E departments.
"Going into the busy winter period, it is important people remember the first port of call for minor conditions or non-emergency medical care should be the local chemist, the 111 helpline, or their GP practice.
"As well as pressures at the hospital 'front door', this month's figures show a 41% increase in delays in being able to discharge inpatients as a result of unavailability of social care, the highest figure ever.
"Going into the holiday period, it is vital local councils, community health services and hospitals work closely to enable older patients to get the support they need after a hospital stay, back at home."
Richard Murray, director of policy at the King's Fund, said: " These figures show the NHS is heading towards a difficult winter, with services under huge pressure and struggling to meet key targets.
"The number of patients ready to be discharged but delayed in hospital continues to increase, with more than 200,000 bed days lost over the course of the month for the first time ever.
"This highlights the impact of social care budget cuts on NHS performance, which is why senior figures from both the health and social care sectors have made the case for the Government to increase funding for social care."
Shadow health secretary Jonathan Ashworth said: "Shamefully, the Tories failed to provide any extra investment for social care in the Autumn Statement last month. Patients deserve better than this, and, with the busy Christmas period approaching, Labour is urging the Government to take immediate action to protect our NHS."
Nick Phin, deputy director of the National Infection Service at PHE, said: "Norovirus is a common cause of illness during winter. Exactly when the peak in activity occurs will be different each winter but levels seen so far this year are not unexpected compared with the previous five years."