Facebook, Twitter and other social media websites boost public awareness of disease outbreaks but also make it more difficult to separate fact from fiction, world health officials said on Thursday.
World Health Organization (WHO) director-general Margaret Chan said the Geneva-based UN body scans websites and online forums in different languages for indications of outbreaks across the world.
Any potential threat is analysed by experts and, if necessary, investigated, she told an international conference in Singapore on improving preparedness to fight disease outbreaks.
"I can assure you that with the rise of social media, the background noises for rumours have become much louder and making it so much harder to detect the really important segments," she said.
"But this development also makes it extremely hard for any country to hide a public health threat of international concern."
Chan, who was director of health in Hong Kong when a fatal outbreak of Severe Acute Respiratory Syndrome (SARS) effectively shut down the territory in 2003, did not elaborate.
China was heavily criticised by the international community during SARS for initially covering up the epidemic, which originated in the south of the country.
The flu-like disease eventually killed more than 800 people worldwide, according to the WHO.
WHO assistant director-general Keiji Fukuda said that during the H1N1 swine flu that swept the world in 2009/2010, the Internet was rife with rumours about how to build immunity against the disease.
"One of the rumours which started was that if you increase your salt intake it can help," Fukuda told reporters on the sidelines of the Singapore conference.
The agency had to counter the rumour, also using social media, by telling readers that taking too much salt "will be dangerous to your health", he added.
"The availability of information is better than in the past, and I think this is positive," Fukuda said.
"On the other hand, in social media anybody can say anything so it's also possible that you have a lot of miscommunication mixed in with correct information."