Richard Knox

A once-a-day pill has been proven to lower the risk of getting HIV among needle-using drug addicts, just as it does among heterosexual couples and men who have sex with men.

Among 2,400 injecting drug users in Bangkok, those assigned to take a daily dose of an antiviral drug Viread, or tenofovir generically, had half the risk of getting HIV over a four-year period as those who took a placebo pill. Among those who took tenofovir faithfully, there were 74 percent fewer infections.

The World Health Organization is warning health care workers everywhere to suspect a disease called Middle Eastern Respiratory Syndrome, or MERS, whenever they see a case of unexplained pneumonia.

Monday's warning comes at the end of a six-day WHO investigation in Saudi Arabia, where 40 of the 55 cases of the respiratory disease have occurred. Sixty percent of those people with known infections died.

The chief of the National Institutes of Health is disavowing a ruling from the government office that oversees the ethics of human research.

Every day in hospitals all over America, thousands of patients die of infections that used to be curable. But the antibiotics used to treat them aren't working anymore.

It's called drug resistance, and it's largely a consequence of antibiotics overuse. The more germs are exposed to antibiotics, the faster they mutate to evade being vanquished.

Thanks to gold-standard tuberculosis treatment and prevention programs, cases of TB in the United States have declined every year for the past two decades — to the lowest level ever.

But TB's course through the Williams family in Boston shows that no nation can afford to relax its efforts to find, treat and prevent TB. It's just too sneaky and stubborn an adversary.

Most women diagnosed with breast cancer when they're 40 or younger are choosing mastectomy rather than more limited and breast-conserving lumpectomy plus radiation, a study of women in Massachusetts finds.

Moreover, most of those choosing mastectomy elect to have the other, noncancerous breast removed, too.

Scientists have completed the first assessments of how readily the H7N9 flu virus in China can pass among ferrets and pigs. The mammals provide the best inkling of how dangerous these bugs may become for humans.

The news is both bad and good. They've found the new bird virus is easily passed between ferrets sharing the same cage.

It's been eight months since a Saudi Arabian doctor described a previously unknown virus related to SARS. And for most of that time only germ geeks paid much attention.

But in the past few days the new virus — which some would like to call MERS-CoV, for Middle East Respiratory Syndrome Coronavirus — has been making up for lost time.

There's been a buzz of activity at the Centers for Disease Control and Prevention in Atlanta since scientists got their first samples of a new bird flu virus from China four weeks ago.

Already they've prepared "seed strains" of the virus, called H7N9, and distributed them to vaccine manufacturers so the companies can grow them up and make them into experimental flu vaccine.

The number of Boston bombing victims still in the hospital dropped to 19 as of Wednesday evening. The great majority have gone home or to a rehab facility.

That's what has happened with Celeste and Sydney Corcoran, a mother-daughter pair who ended up in the same hospital room after being struck down by the first marathon bomb blast.

Forty-seven-year-old Celeste Corcoran is propped up in her hospital bed. In a nearby window is a forest of blooming white orchids from well-wishers. On the opposite wall, a big banner proclaims "Corcoran Strong."

She's recalling how thrilled she was to be near the finish line of the Boston Marathon, waiting for her sister Carmen Accabo to run by. "I just remember standing there, wanting to be as close as I could to catch her," Corcoran says. "I really just needed to see her face."

The largest current study of an AIDS vaccine, involving 2,500 people, is being stopped.

After an oversight committee took a preliminary peek at the results this past Monday, they concluded there was no way the study would show that the vaccine prevents HIV infection.

Nor would the vaccine suppress the wily virus among people who get infected despite being vaccinated.

The work is only in mice so far, but it sure is intriguing.

A newly found hormone revs up production of cells that make insulin — the very kind that people with advanced diabetes lack.

An international dream team of flu experts assembled in China today.

Underscoring the urgency that public health agencies feel about the emergence of a new kind of bird flu, the team is headed by Dr. Keiji Fukuda, the World Health Organization's top influenza scientist.

Before he left Geneva, Fukuda explained the wide-open nature of the investigation in an interview with NPR.

Boston hospitals always staff up their emergency rooms on Marathon Day to care for runners with cramps, dehydration and the occasional heart attack.

But Monday, those hospitals suddenly found themselves with more than 100 traumatized patients — many of them with the kinds of injuries seen more often on a battlefield than a marathon.

Like most big-city hospitals these days, Tufts Medical Center runs regular disaster drills, featuring simulated patients smeared with fake blood.

A precious package arrived at the Centers for Disease Control and Prevention last Thursday afternoon.

Inside, packed in dry ice to keep it frozen, was a vial containing millions of viruses derived from a 35-year-old Chinese housewife who died last Tuesday of respiratory and kidney failure.

Federal officials say a large study of premature infants was ethically flawed because doctors didn't inform the babies' parents about increased risks of blindness, brain damage and death.

The study involved more than 1,300 severely premature infants at nearly two dozen medical institutions between 2004 and 2009. The infants were randomly assigned to receive two different levels of oxygen to see which was better at preventing blindness without increasing the risk of neurologic damage or death.

Sixteen cases of a new flu around Shanghai have touched off a major effort to determine what kind of threat this new bug might be.

The victims range in age from 4 to 87 years old. Six have died. It is a tragedy for them and their families, but is it a global crisis?

To understand why so few cases are generating so much concern, the first thing to know is that no flu virus like this one — called H7N9 — has ever been known to infect humans before.

Most people (including a lot of doctors) think of a stroke as something that happens to old people. But the rate is increasing among those in their 50s, 40s and even younger.

In one recent 10-year period, the rate of strokes in Americans younger than 55 went up 84 percent among whites and 54 percent among blacks. One in 5 strokes now occurs in adults 20 to 55 years old — up from 1 in 8 in the mid-1990s.

The largest gene-probing study ever done has fished out dozens of new genetic markers that flag a person's susceptibility to breast, ovarian and prostate cancer.

The 74 newly discovered genetic variants double the previously known number for these malignancies, all of which are driven by sex hormones.

Underscoring the sheer magnitude of the findings, they're contained in 15 scientific papers published simultaneously by five different journals. The Nature group of journals has collected them all here.

Mammography outcomes from nearly a million U.S. women suggest which ones under 50 would stand the greatest chance of benefiting from regular screening: those with very dense breasts.

That's been a bone of contention ever since a federal task force declared nearly four years ago that women younger than 50 shouldn't routinely get the test.

Nothing sends more kids to the hospital than asthma.

So when doctors at Children's Hospital in Boston noticed they kept seeing an unusually high number of asthmatic kids from certain low-income neighborhoods, they wondered if they could do something about the environment these kids were living in.

Just last week AIDS researchers were excited about a Mississippi toddler whose blood has remained free of HIV many months after she stopped getting antiviral drugs – what doctors call a "functional cure."

Every day something like 550 hospitalized Americans suffer cardiac arrest. That's bad news. Only about one in five will live to leave the hospital.

But for the lucky 44,000 a year who are resuscitated and survive, the outlook is much better than expected, authors of a new study say.

Picture this: Your spouse or child has collapsed and isn't breathing. You call 911, and the paramedics rush in and take charge. But you are banished to another room while the medical people try to bring your loved one back to life.

It's about the most stressful scene imaginable. And it's what usually happens.

It's not the first study that finds the lowly aspirin may protect against the deadliest kind of skin cancer, but it is one of the largest.

And it adds to a mounting pile of studies suggesting that cheap, common aspirin lowers the risk of many cancers — of the colon, breast, esophagus, stomach, prostate, bladder and ovary.

We don't know too much about a Nepalese man who's in medical isolation in Texas while being treated for extensively drug-resistant tuberculosis, or XDR-TB, the most difficult-to-treat kind. Health authorities are keen to protect his privacy.

But we do know that he traveled through 13 countries — from South Asia to somewhere in the Persian Gulf to Latin America — before he entered the U.S. illegally from Mexico in late November. He traveled by plane, bus, boat, car and on foot.

Scientists believe a little girl born with HIV has been cured of the infection.

She's the first child and only the second person in the world known to have been cured since the virus touched off a global pandemic nearly 32 years ago.

Doctors aren't releasing the child's name, but we know she was born in Mississippi and is now 2 1/2 years old — and healthy. Scientists presented details of the case Sunday at a scientific conference in Atlanta.

There's great enthusiasm among some global health leaders about a bold – some say radical — strategy to prevent pregnant women from transmitting HIV to their newborns.

But skeptics worry that the approach, dubbed Option B+, will pit pregnant women with HIV against others infected with the virus, diverting resources from the broader struggle against the pandemic.

Researchers say more young American women are being diagnosed with advanced breast cancer.

It's a newly recognized trend. The numbers are small, but it's been going on for a generation. And the trend has accelerated in recent years.