China is witnessing an alarming increase in the number of babies born with syphilis, a potentially fatal disease that experts say was virtually wiped out five decades ago.

Research shows cases have risen sharply in the last 10 years -- and in coastal cities, such as Shanghai, it is ranked as one of the most commonly reported sexually transmitted diseases (STDs).

The rate of increase is unprecedented since the introduction of penicillin. But it is the soaring number of newborn sufferers that has sparked the greatest concern, say analysts.

A total of 9,480 babies were born with congenital syphilis in 2008, more than one each hour, according to research published last month by the New England Journal of Medicine. A separate study in the Lancet, another well-respected journal, said the figure had risen by more than 70 percent year on year since 1991.

Liu Gang (not his real name), a 40-year-old farmer from Shenyang in Liaoning Province, learned that his new son had the disease in February a month after his wife died during delivery. "I felt like the sky had collapsed on top of me," he told China Daily.

"When I first saw the (baby's) symptoms, I was a little surprised," said Li Lingyun, deputy director of dermatology at Shenyang No.7 Hospital, where Liu's son was treated. "He had little red spots almost everywhere on his body, particularly his forehead, groin and armpits."

Blood tests showed Liu's wife was suffering syphilis during pregnancy, but the family had no idea until after her death. Depending on the length of time of the infection, the disease can cause pregnant women to go into premature labor and increase the risk of stillbirth.

Doctors say the syphilis bacterium can also easily pass from mothers to embryos in the womb through the placenta.

Without urgent treatment, child sufferers - many of whom are born without obvious symptoms -- are prone to serious development problems and seizures, and have only a 50-percent chance of surviving infancy, according to research in the New England Journal of Medicine.

Although syphilis is difficult to diagnose, experts blame the staggering increase on shortcomings in the country's screening process, and have urged more couples to carry out pre-marital and pregnancy health checks to catch potential dangers early on.

"The lack of compulsory periodic screening for pregnant women, as well as people's ignorance of syphilis symptoms, is resulting in an increasing number of women giving birth to syphilis-infected children," said Wan Shaoping, a professor at the Sichuan Institute of Dermatology and STD Prevention.

Pre-marital check-ups were switched from being mandatory to voluntary in 2003, "but that does not mean they are not important", said Wan, who called on authorities to do more to raise awareness of antenatal diagnosis, genetic counseling and other preventive technical services.

A couple in their late 20s whose 1-month-old son was diagnosed with syphilis in Wuhan, capital of Hubei Province, admitted they did not undergo health checks before they tied the knot or during the pregnancy.

They were only alerted to the child's condition by the fact he was unable to move his right wrist, which was red and swollen.

"From his symptoms, we suspected it might be syphilis-related bone damage," said Zhao Min, an associate chief physician at Wuhan Institute of Dermatology and STD Prevention.

Although the disease was transmitted to the boy through his mother, blood tests show his father was the first to be infected. "The couple was full of remorse," said Zhao. "If they had done checks either before marriage or during pregnancy, the virus could have been found before it was transmitted to their child."

Zhou Hongyu, director of education at Huazhong Normal University and a member of the National People's Congress, the nation's top legislative body, has proposed offering free check-ups to couples in more cities and regions.