A US hospital had to turn away patients last week after being hit by a “virus” infection that downed the institution’s network and sent staff back to using paper records.

The unidentified malware started to cause problems for the Gwinnett Medical Center in Lawrenceville Georgia last Wednesday and got progressively worse until the hospital was forced to divert all non-emergency admissions to other medical centres.

By Friday night, the IT team had the outbreak under control and by Saturday were able to go back to using the computerised records system, local media reported.

The source of the outbreak – not the first that has affected the hospital according to sources – is still not clear, nor has the malware been identified beyond it being described generically as a “virus.”

"We actually have some of our IT vendor partners that are on site with us that have actually been here since Wednesday. We've also got internal teams that are trying to identify the virus issues," said Gwinnett Medical Center spokesperson, Beth Okun.

"It's not affecting patient care in any way, shape or form," she said adding that patient data had not been at risk.

Given the symptoms mentioned in reports, a worm infection (for example by Conficker or one of its variants) seems the most likely cause, which could have spread rapidly across the hospital’s network forcing IT to pull connectivity to avoid it spreading further with unknown consequences.

The standard procedure for a fast-spreading worm is immediate isolation followed by a hunt for the point at which the malware entered the network, most likely a laptop or USB stick brought into the hospital by a member of staff.

The events bear a striking resemblance to a similar problem that hit New Zealand’s St John Ambulance Service a fortnight ago.  That attack disrupted the ambulance communications system, forcing administrators to revert to manual radio contact to direct staff to emergencies.

As with any organisation using Windows-based PCs, hospitals are regularly afflicted with malware but it is still unusual for institutions to find themselves disrupted seriously enough for the fact to become public.

In 2008, admissions systems at three hospitals in London had to be shut down after 4,700 computers became infected with the Mytob worm first detected by security companies three years earlier.

A security report on the incident later described the worm infection as "entirely avoidable," and as having been caused by a number of factors including poor management of antivirus updates on the affected machines.

Mytob acquired a reputation for potency. In a separate discovery, a variant was found that spread by posing as a message from the IT administrator.