Two patients, including a medical worker, being treated for the H7N9 strain of avian flu, died in Shanghai, local health authorities revealed on January 20.

Both tested posthumously positive for the H7N9 virus, according to the Shanghai Municipal Commission of Health and Family Planning.

The agency said that it was conducting further investigation and trying to track the source of the infection.

Shanghai has confirmed seven human H7N9 cases so far this year.

Zhejiang, a province located south of Shanghai, reported six more cases of H7N9 on January 19 and 20.

The new cases brought the number of infections in Zhejiang since the new year to 26, the most nationwide, according to the Zhejiang Provincial Commission of Health and Family Planning.

Human infections of H7N9 have also been reported in Jiangsu, Fujian and Guangdong provinces.

The southern province of Guangdong reported its third H7N9 death of this year on January 20.