In the aftermath of the earthquake in Japan, Twitter is proving "an excellent system" for communicating with chronically-ill patients, say doctors.

In letters written to The Lancet, Japanese doctors say social networking sites have been vital in notifying patients where to get medication.

Although telephone networks were disrupted after the earthquake, internet access remained reliable.

But Japan must now strengthen its primary care system, they said.

The letters, which appear in the Correspondence section of The Lancet, were written by Japanese doctors across the country.

They talk about the health care consequences of the earthquake and tsunami disaster which occurred in Japan in March.

In one letter, Dr Yuichi Tamura and and Dr Keiichi Kukuda, from the department of cardiology at Keio University School of Medicine in Tokyo, described their initial concern over how to get drugs to patients with pulmonary hypertension after the disaster.

"Forming a supply chain for such drugs in the earliest stages of the disaster was difficult; however we found that social networking services could have a useful role."

Using the 're-tweet' facility on Twitter allowed information to be spread rapidly, they said.

"We were able to notify displaced patients via Twitter on where to acquire medications. These 'tweets' immediately spread through patients' networks, and consequently most could attend to their essential treatments."

On the move

But they also needed the hands-on help of countless medical staff to deliver drugs and oxygen.

"Our experience has shown that social networking services, run concurrently with physical support, were significant in triumphing over many difficulties in the recent catastrophe," they wrote.

In another letter, doctors describe how they transferred 600 dialysis patients from the area near the Fukushima nuclear power plant over 200km to another city to receive the urgent care they needed.

The patients were unable to bring their medical records with them on the journey from Iwaki to Niigata in the north west of Japan.

Dr Junichiro James Kazama, from Niigata University Hospital, said his team's experience of two previous earthquakes helped in the mass transfer.

"The transfer of 600 haemodialysis patients is an unprecedented event.

"However this mass relocation seems to be merely the beginning, because the accident recovery operation is still underway at the Fukushima Daiichi nuclear power plant," Dr Kazama wrote.

In other letters, doctors criticised the weakness of the Japan's primary care system, saying that patients normally have to go straight to hospital if they want to be treated for anything.

After the earthquake and tsunami, this situation created chaos.

"Hospitals were unable to tend to patients with non-urgent but important needs such as treatment of hypertension, diabetes, gastroenteritis, and so forth. Japan needs to strengthen its primary-care system," wrote Dr Jay Starkey from the University of Iowa and Dr Shoichi Maeda from Keio University in Tokyo.