West Middlesex University Hospital NHS Trust has become the latest NHS trust to be infected by the Conficker worm.
The trust was hit on 11 February and had to shut down its entire network to isolate virus and clean the system.
Although the trust managed to get a number of computers working in priority areas such as A&E, ITU, theatres and outpatient departments within a few days, it has had to resort to using manual systems.
A statement provided to E-Health Insider said: “Our main priority has been to ensure the delivery of safe patient care.
"Shutting our network down has caused some operational issues. However, we implemented our business continuity plans and operated manual systems as part of our standard contingency plan.”
“We have been working hard to restore our systems and to date we have cleaned the majority of PCs in the trust, resulting in the majority of inpatient and outpatient areas returning to normal working.”
The trust has continued to warn patients that they are likely to face delays whilst staff try to catch up by using the manual system.
The statement adds: “We continue to ask that patients only contact the hospital for urgent requests until our systems are fully operational.”
The trust said that it has an active antivirus system in place and precautions have been put into place to prevent a similar attack.
It has also launched an investigation into the incident to implement lessons learnt to avoid a recurrence and to provide learning for other NHS organisations.
In January, Mid Cheshire Hospitals NHS Foundation Trust was hit by the Conficker worm, which affected around 3% of the trust’s computers.
Following that, NHS Leeds was also affected by Conficker, which forced administrators to take around 10 servers offline. According to the trust, PCs were not affected by the attack which was thought to have come from an old infected laptop.