Sad news out of Maryland, and a reminder of how devastating MRSA, methicillin-resistant Staphylococcus aureus, can be when it combines with flu infection. According to the Maryland Department of Health and Mental Hygiene, the Washington Post and ProMED, five members of a family have fallen ill and three have died from MRSA pneumonia that took hold in lungs inflamed by flu infection.

The dead are Ruth Blake, 81, and her children Lowell, 58, and Vanessa, 56. Another child, Elaine, also fell ill and was hospitalized, and Ruth Blake’s sister has been hospitalized also. They had all contracted one of the seasonal flu strains circulating this year: H3N2. According to the Post, Ruth Blake was vaccinated against flu this season; her children were not. The assumption is that both flu and MRSA spread from the mother to the children.

From the Post:

Calvert health officials said in a statement Wednesday that the cases were isolated to a single family and that “there are currently no other affected individuals.” Local health-care providers, they said, are not reporting any significant increase in patients with flulike symptoms.

David Rogers, the county’s health officer, said health officials suspect that Blake also had the flu and then suffered a serious lung infection that turned into pneumonia.

“In older people, that can often be fatal,” he said.

Blake had a flu shot, he said. None of the others were vaccinated.

What’s unusual, he said, is that the infection spread from the mother to three children, probably at her bedside. Most likely, the mother’s coughing spread the virulent organisms into the air, and her caregivers, two of whom also had the flu, breathed them in and became infected, he said. (Byline: Annys Shin and Lena H. Sun)

MRSA pneumonia is fast-acting and lethal; it is often called “necrotizing pneumonia” for the way it simply kills lung tissue. Exactly why it has that effect is still disputed — MRSA has so many cellular toxins at its disposal that there could be a number of culprits — but there is no dispute that it is a very serious disease.

MRSA post-flu pneumonia isn’t well-understood because it has been a concern only recently. The first cases to alert the United States this might be a problem were in Baltimore in the flu season of 2003-04. The four patients were all seen at Johns Hopkins University Medical Center, and physicians there wrote the cases up afterward. Over two months, there was a 31-year-old woman who was in the hospital for four weeks; MRSA ate holes in her lung, the largest of which was 1 by 1.5 inches. Two other women, 20 and 33 years old, were each hospitalized for three months. The 20-year-old’s heart stopped, and her blood clotting grew so disordered that doctors had to amputate one leg below her knee; the 33-year-old lost both lower legs. The fourth patient was a 52-year-old man, a two-pack-a-day smoker, who died.

Other reports came into the Centers for Disease Control and Prevention over the course of that flu season. When the CDC counted up the following summer, there had been 15 cases of severe MRSA pneumonia in 9 states. Four of them died. CDC personnel wrote another article warning of the dangers of MRSA and flu two years later, after clusters of cases in Louisiana and Georgia during the 2006-07 flu season. They said: “Secondary S. aureus pneumonia is a potentially catastrophic complication of influenza… MRSA [community-acquired pneumonia] often affects young, otherwise healthy persons and can be rapidly fatal.”

Pneumonia that follows on flu is a seriously under-appreciated danger of flu infection: An analysis from 2010 points out that, in 2007, there were 457 deaths from flu in the US and 52,847 deaths from post-flu pneumonia. There is no reliable way to protect yourself against MRSA, since there is no vaccine, and the bacterium can live on the skin undetected for an unpredictable period of time. Hypothetically, if you prevent flu infection you lessen the likelihood of this pneumonia occurring — but as the mother’s case illustrates, flu vaccine doesn’t confer perfect protection, especially not in the elderly whose immune systems are not robust enough to begin with.

It’s a very sad story, and another illustration of how perilous and destructive MRSA can be.

What's unusual, he said, is that the infection spread from the mother to three children, probably at her bedside.

Most likely, the mother's coughing spread the virulent organisms into the air, and her caregivers, two of whom also had the flu, breathed them in and became infected, he said.

(CNN) -- The Calvert County investigation into the flu deaths of 3 family members in Lusby, Maryland, found two of them--a 58 year-old brother and his 56-year-old-sister died of serious lung infections, a complication of seasonal flu.

The CDC already has confirmed the siblings died of influenza A. The strain is still unknown. Their 81-year-old mother, who was being cared for by her three children died at home Thursday of complications from the flu. The surviving sibling, a 51-year-old woman, remains in guarded condition at MedStar Washington Hospital Center in Washington, D.C., where she is responding to treatment.

Dr. David Rogers, Health Officer of Calvert County, says the investigation into the flu deaths of the three family members in Lusby, Maryland, is continuing. Rogers told CNN while unusual, these were isolated cases and the community at large should not be overly concerned or alarmed.

"This is extremely rare. I think what happened here is that we had an elderly woman who got flu, then she suffered a complication of flu, a severe bacterial pneumonia. Three kids came to provide bedside care and came in close contact. They may not only have caught flu from her but the serious lung infection that she had." Rogers said. "This is a very isolated situation where you have four people in a home, in close contact. This happens not infrequently in elderly people."

The Centers for Disease Control and Prevention estimates 90% of seasonal flu related deaths and more than 60% of flu related hospitalizations in the United States each year are in people 65 or older.

The sister of the deceased 81-year old woman is now also being treated for flu like symptoms at MedStar Washington Hospital Center.

Dr. Janis Orlowski, Senior Vice President and Chief Medical Officer at MedStar Washington Hospital Center, says the woman was admitted last night and is in fair condition.

"We don't yet know what this is about," Orlowski said. "She has a fever and a cough. They were all together at a funeral last week. Individuals could easily have caught the flu--a large gathering of people, hugging, consoling, possibly sharing a meal."

"If the individuals had the flu at that time it is quite likely that others are showing signs of the flu," says Orlowski. 'If I was in that family and felt ill, I would seek medical attention early."

Orlowski also treated the brother, who passed away at the hospital Monday night.

She says the bacterial infection they had was a staphylococcal (staph) infection, which she calls a super infection. Cultures on the surviving sister are not back yet. The source of the staph is still unknown, but Orlowski says the bacteria is naturally on the body. On skin, in the nose. Most people, she says, don't catch it from someone else.

"The question is did the mother have the staph where it went to the hands of the children and they got infected or did each end up becoming super infected with their own bacteria and we don't know the answer to that. It's likely we will never know."

And rare enough that they looked for other sources.

"We did look for poison, carbon monoxide in the house, did they all ingest something?" Orlowski asks. "It's astonishingly rare, such that we are all looking that other explanations."

Orlowski says over the last several days the hospital emergency room filled with nearly 400 patients. Most had chronic illnesses like heart failure, chronic obstructive pulmonary disease (COPD) and liver disease made worse by a bout of flu.

"It's flu season in the mid-Atlantic area so I urge the public to get vaccinated if you have not been, wash your hands, and if you are ill, don't go to school or work. We don't want you to spread the illness."