A 61-year-old woman from Langfang, Hebei province, is in critical condition after being infected with the H7N9 virus, the latest known case of bird flu on the mainland.

The woman is in an intensive care unit in Beijing Chaoyang Hospital.

The intensive care unit at Beijing Chaoyang Hospital admitted a woman from Hebei province on Thursday who later tested positive for the H7N9 strain of bird flu, health authorities in Beijing said. Her condition has not improved, doctors said. Liu Chang / For China Daily

She displays symptoms of viral pneumonia, acute kidney failure, acute respiratory distress syndrome, septic shock and diffuse intravascular coagulation.

The patient is said to have visited a food market where live poultry is sold each day from June 30 to July 9, the Beijing Health Bureau said.

She had a fever on July 10. On July 13, she sought treatment in a community healthcare center in Langfang.

She was later admitted into another hospital, but her condition worsened despite being given antibiotics. She was transferred to Chaoyang Hospital on Thursday.

Beijing's Center for Disease Control and Prevention confirmed on Saturday morning that the woman was infected with H7N9.

Her health worsened on Sunday, Chaoyang Hospital said, and she was moved to a single-person ICU room and assigned special workers to take care of her.

The hospital said it has tested people in close contact with the woman, including family members and medical workers, and has given them preventive medication.

None of these people has tested positive for the virus or showed any symptoms.

It is about two months since hospitals in Beijing took in a 6-year-old boy infected with H7N9.

The woman is the first diagnosed case of H7N9 infection in Hebei province, and the first such case in China since July.

Zhao Bo, an official from the health bureau in Langfang, said they have tested the live poultry in the market the patient went to and a sample tested positive for the virus.

The market has been closed and the other live poultry markets in the city center were also suspended.

Hebei province's health bureau has dispatched an emergency team to Langfang, and has asked the city to keep track of the conditions of the patient and the people who were in close contact with her.

Hu Bijie, an infectious diseases expert in Zhongshan Hospital in Shanghai, said the case seems "odd".

"Theoretically speaking, such a case is very unlikely to occur in summer," he said. "The monitoring of the H7N9 cases in the past few months has also shown that the number of new cases decreases as the temperature gets higher."

The prevalence of H7N9 infection reached its height in April, when new cases were reported almost daily. The number of new cases sharply decreased in May, and only one case was reported in June.

Also, experts found that people older than 60 fall victim more easily to H7N9.

"The reason, we suspect, is that older people have weaker immune systems, and they are usually retired, tend to go to food markets more often, and are more willing to buy and process live poultry than younger people," said Hu.

He Xiong, deputy director of Beijing's Center for Disease Control and Prevention, said the case will not change the city's strategy in preventing and controlling H7N9, where all the cases of pneumonia without identified causes are tested for possible viruses, including H7N9.