During the 2003 Iraq invasion, NBC correspondent David Bloom called his wife, Melanie, from the top of an Army tank that he had been riding in for several days.

Melanie Bloom is raising awareness for deep-vein thrombosis, the disorder that killed her husband, NBC journalist David Bloom. By Todd Plitt, USA TODAY

He was whispering.

"I asked why, and he said, 'Oh, we're on the border of Baghdad, and we have to whisper because of the risk of ambush,' " Melanie Bloom says. "And I said, 'Then why are you sleeping outside on top of the tank, not in the tank?' He said, 'My legs have been cramping up, and I really have to stretch them out tonight.' It sounded so innocuous."

Two days later, on April 6, Bloom, 39, died from a pulmonary embolism — a blood clot that moved from the leg to the lung — caused by a condition called deep-vein thrombosis. DVT can occur when people have certain risk factors coupled with restricted mobility.

In Bloom's case, those factors included several long flights between New York and Kuwait as war brewed, a genetic disposition to clots, and ultimately being dehydrated and riding in a cramped tank for hours on end without being able to move.

"The hardest thing I've ever had to do in my entire life was sit our three girls down (twins Christine and Nicole, now 11, and Ava, now 6) and tell them they'll never see their daddy again," Bloom says. "I had steeled myself against the dangers of war, but to hear that he had passed away from these words that I had never heard before and didn't know anything about, I just didn't understand how this was possible."

It took about a year "to come out of the utter raw grief," Bloom says. But when she did, she decided to devote time to educating the public about DVT. About 2 million Americans each year develop DVT, and it kills 200,000 of them — more than breast cancer and AIDS combined.

Today, Bloom and the Coalition to Prevent Deep Vein Thrombosis (sponsored by Sanofi-Aventis, which makes a blood-thinning drug called Lovenox) kick off events in New York, Miami and Washington to call attention to DVT (preventdvt.org).

"David's life was dedicated to informing the public, and so in a sense I am trying to champion his legacy by doing just that and informing the American people about that which took his life," Bloom says. "If one person hears this and lives, if one life is saved, then David's death is not in vain."

Her daughters are doing well, Bloom says, and at a recent school science symposium, Christine and Nicole devoted their project to DVT. "Parents who came by their board would tear up, and they were standing there like little soldiers, trying to comfort them."

The night Bloom learned of her husband's death came rushing back on Jan. 29, when ABC News anchor Bob Woodruff was seriously wounded by a roadside bomb in Iraq. "It was terrifying. I thought I was dreaming," Bloom says.

The Blooms and Woodruffs — individually and as couples — had been close friends ever since they all met at a roast for CNN's Larry King years ago in Washington.

When Woodruff was injured, ABC was unable to reach Woodruff's wife, Lee, and Bloom was called to help find her. Bloom did, just as Woodruff had done the night NBC News could not reach her because she had turned off the phone to get some sleep.

Bloom accompanied Woodruff to the U.S. military hospital in Landstuhl, Germany, and is in close touch with Lee Woodruff.

"It was my turn to help her," Bloom says. "Lee was a rock for me when I lost David, and she was really by my side every minute."

Last week in an e-mail, Lee Woodruff told Bloom that her husband continues to get better and that there is hope for a full recovery.

"We are so encouraged by all the things he is doing, from hugging and kissing to communicating with us," Woodruff wrote. "His physical strength remains impressive, and his doctors are so encouraged by the progress he has made."

Bloom says that her husband's death and Woodruff's injury are reminders that "life is precious and fleeting and we all need to cherish the ones we love, because life can change on a dime."

"It's not just Lee and it's not just me who are going through this," Bloom says. "There are so many people going through this very thing, with the world climate that it is today — with terrorism, the war, with Katrina and other natural disasters.

"It's a tough world that we live in right now. But I think we all need to count our blessings and to tell our kids we love them every day. It sounds so trite and so clichéd, but it is so true."