Two hospitals in Northamptonshire said patients had been put "at risk" by people with suspected swine flu visiting accident and emergency (A&E).
Kettering General and Northampton General said 11 people with swine flu symptoms had visited in the past week.
It advised people to stay at home and seek advice from NHS Direct.
"Patients in A&E waiting rooms can be very ill, and catching swine flu could make them a lot worse," said Kettering consultant Dr Nathan Spencer.
Helen O'Shea, deputy chief executive at Northampton General, said A&E departments in Northamptonshire cannot issue anti-viral medication.
"The best thing for people who think they need further treatment is to seek expert advice for their individual circumstances by using the national helplines or the internet," she added.
Visiting times at both hospitals have been restricted to an hour each day.
Pregnant visitors, those with suppressed immunity and children under five are not permitted.