U.S. teen births have dropped to a record low, but the country still has one of the highest rates among developed nations, the U.S. Centers for Disease Control and Prevention said Thursday.

"The overall rate declined 25 percent from 41.5 per 1,000 teenagers aged 15-19 in 2007 to 31.3 in 2011 -- a record low," the CDC report said.

Top AIDS scientists were optimistic Wednesday of finding a cure for the disease that has claimed 30 million lives -- but said it might not work for all people.

The experts have high hopes for a treatment that will be given at an early stage of infection -- most likely a cocktail that includes an immunity booster and a virus killer.

Scientists said Tuesday they had managed to kill lab-grown tuberculosis (TB) bacteria with good old Vitamin C -- an "unexpected" discovery they hope will lead to better, cheaper drugs.

A team from Albert Einstein College of Medicine in New York made the accidental find while researching how TB bacteria become resistant to the TB drug isoniazid.

A Japanese cancer specialist said Wednesday she has started the world's first clinical trial of a powerful, non-surgical, short-term radiation therapy for breast cancer.

The National Institute of Radiological Sciences has begun the trial using "heavy ion radiotherapy" which emits a pinpoint beam that can be accurately directed at malignant cells, said Kumiko Karasawa, radiation oncologist and breast cancer specialist.

The world is unprepared for a massive virus outbreak, the deputy chief of the World Health Organization warned Tuesday, amid fears that H7N9 bird flu striking China could morph into a form that spreads easily among people.

Keiji Fukuda told delegates at a WHO meeting that despite efforts since an outbreak of another form of avian influenza, H1N1, in 2009-10, far more contingency planning was essential.

An experimental sleeping pill from U.S. drug company Merck is effective at helping people fall and stay asleep, according to reviewers at the U.S. Food and Drug Administration, which could soon approve the new drug.

But the experts warned of dangerous side effects at high doses -- including residual sleepiness during the day and, in a small number of subjects, suicidal thoughts -- according to their report posted Tuesday.

A 66-year-old Tunisian man has died from the new coronavirus following a visit to Saudi Arabia and two of his adult children were infected with it, the Tunisian Health Ministry reported.

His sons were treated and have since recovered but the rest of the family remains under medical observation, the ministry said in a statement Monday. The World Health Organization confirmed the cases of the children, but said one of them was a daughter who was with her father for part of the trip to Saudi Arabia and Qatar. There was no immediate way to reconcile the differing reports.

A Saudi man who had contracted the coronavirus has died, raising the death toll in the kingdom from the SARS-like virus to 16, the health ministry announced on Monday on its Internet website.

"One of the patients who had contracted the virus has died," in the Eastern Region of Saudi Arabia where most of the kingdom's cases have been registered, the ministry said.

A Nobel prize-winning scientist Tuesday played down "shock-horror scenarios" that a new virus strain will emerge with the potential to kill millions of people.

Peter Doherty, who jointly won the Nobel prize in 1996 for his work on how the immune system combats virus-infected cells, said the worst-case scenario was a new virus with a high mortality rate that was also highly infectious.

No new human cases of the H7N9 virus have been recorded in China for a week, national health authorities said, for the first time since the outbreak began in March.

One previously infected patient died in the week beginning May 13, the National Health and Family Planning Commission said in a statement late Monday, taking the total number of fatalities from the virus to 36.