Geneva, Switzerland - The World Health Organization (WHO) on Thursday gave the all-clear, for the time being, in regards to an unusual cluster of following consultations with local authorities.

Chinese health authorities told the WHO in a teleconference that they had not discovered any unusual or new pathogens or unusual clinical pictures, the organization said in Geneva late on Thursday.

On Wednesday, the WHO had asked China to provide "additional epidemiologic and clinical information" on the diseases involved and their spread, as well as laboratory results, the international body said.

The illnesses were caused by several known respiratory pathogens, including rhinoviruses, RSV (respiratory syncytial virus), and mycoplasma infections (Mycoplasma pneumoniae), the Chinese authorities told the WHO.

The data showed "an increase in outpatient consultations and hospital admissions of children due to Mycoplasma pneumoniae pneumonia since May, and RSV, adenovirus and influenza virus since October," the WHO said in a statement.

These are cell wall-deficient bacteria that only occur in humans and are present worldwide. They can cause tracheobronchitis or pneumonia, especially in children and adolescents. These bacteria are resistant to certain antibiotics, but according to the WHO, they can be treated with other antibiotics.

"Some of these increases are earlier in the season than historically experienced, but not unexpected given the lifting of COVID-19 restrictions, as similarly experienced in other countries," the WHO said, adding it would continue to communicate with Chinese authorities and monitor the situation.

That echoes a statement from China's National Health Commission attributing the increase in respiratory illnesses in the country to the spread of known pathogens following the lifting of the coronavirus measures.

Other countries also experienced particularly strong waves of colds after they lifted coronavirus restrictions.

The WHO had requested information from China after an increase in respiratory diseases in northern China came to light. The media had reported an increase in undiagnosed pneumonia among children in the region.

Reports and pictures of full children's hospitals have been circulating on China's social media for days. The WHO recommended that China continue to monitor the cases.

The organization recommended that people get vaccinated against influenza and Covid-19 if possible, stay away from sick people and self-isolate if they are ill, wear face masks if necessary, ensure good ventilation, and wash their hands regularly.

"WHO does not recommend any specific measures for travellers to China. In general, persons should avoid travel while experiencing symptoms suggestive of respiratory illness, if possible," the world body said.