Dear Doctor: It seems like every time we turn on the TV there's another recall of romaine lettuce because of another outbreak of E. coli. What's the deal? How dangerous is it if I get infected?

Dear Reader: You're right -- there seems to be no end in sight to the safety issues having to do with romaine lettuce and E. coli bacteria. It's understandable that there would be occasional safety issues in a food supply chain as vast and complex as the one that serves the United States. When it comes to romaine lettuce, though, the ongoing issues seem to be in a category all their own.

Let's start with E. coli, the bacteria that's causing salad lovers so much trouble. The full name is Escherichia coli, and it comes in many different strains, which live in the intestines of humans and animals. Most strains are harmless and co-exist peaceably with their hosts. However, some strains produce something known as Shiga toxin, a particularly nasty pathogen. Once the "bad" E. coli strains are ingested and reach the large intestine, they multiply rapidly. They then bind to the intestinal lining, which is rich in tiny capillaries. That gives the Shiga toxin a pathway to the kidneys.

The inflammation resulting from the presence of Shiga toxin is believed to cause the initial symptoms, which begin with abdominal cramping that can become quite severe. The diarrhea that follows often becomes visibly bloody. Sometimes this is accompanied by vomiting or, less commonly, fever. The incubation period is anywhere from one to 10 days, but most people become ill within three to four days of infection. This occurs when someone ingests contaminated food or drink, and through the oral-fecal route. The illness lasts anywhere from a few days to close to two weeks. For most, E. coli infection is extremely unpleasant but not life-threatening. But for young children and the elderly, such an infection can be fatal. That's because they are at increased risk of developing hemolytic uremic syndrome, a form of kidney failure.

As for why romaine lettuce appears to be susceptible to infection with E. coli, the reasons aren't completely clear. One outbreak was thought to be caused by water that flowed through an irrigation canal believed to be contaminated by the bacterium. In some cases, infections have been traced back to livestock operations that border fields of romaine. Other points of potential infection are processing facilities, where romaine is washed and bagged. The lettuce industry has pledged mitigations to address each of these issues, particularly those having to do with contaminated irrigation water.

In the meantime, it's vital to abide by the Food and Drug Administration's directives to steer clear of romaine. It may be tempting to keep whatever you have in your fridge and simply wash it thoroughly. Unfortunately, that won't work. E. coli can hide in microscopic crevices, and it's impossible to get rid of it all. In fact, the CDC recommends that consumers thoroughly clean the place in the refrigerator where the contaminated food was stored.

For the latest updates regarding food-borne illnesses and contaminants, including the romaine recalls, visit www.fda.gov/Food.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: Pretty much everyone I know gets cold sores from time to time. Now I see a study saying that cold sores are somehow connected to Alzheimer's. Can you explain?

Dear Reader: As researchers have worked to understand Alzheimer's disease, the results of some studies have suggested a link to certain infections, including oral herpes, or cold sores. Pneumonia, chronic inflammation and infection with spirochete bacteria, which causes Lyme disease and can be associated with some types of gum disease, were implicated as well. Initially scientists noticed a higher incidence of Alzheimer's among people who also reported having contracted one or more of these infections. It was unclear whether the infections themselves were linked to Alzheimer's, or whether people with Alzheimer's were simply more prone to infection.

Now, a new study draws a clearer line between Alzheimer's disease, a devastating form of dementia, and the herpes simplex virus 1, which causes cold sores. Published last fall in the journal Frontiers in Aging Neuroscience, the study cited being infected with herpes simplex virus 1, also known as HSV1, as a major risk factor for developing Alzheimer's disease. In the new study, which consists of a review of decades of research, including her own, a scientist from England's University of Manchester thinks that up to half of all cases of Alzheimer's disease have a direct connection to HSV1.

An estimated 5.7 million Americans are now living with Alzheimer's, with a new diagnosis being made every minute. At this time there is no cure for the disease, and no reliable ways to manage it. When it comes to HSV1, between 50 and 80 percent of adults in the United States are believed to be infected with the virus. It is spread through contact with the oral secretions of someone who has an active infection, whether through direct contact or by sharing an object, like a glass or a toothbrush. Once infected, a person has the virus for life. However, much of the time it lies dormant. Some people can have the virus and never develop symptoms. Others can have outbreaks that range from occasional to frequent.

The thinking behind the link between HSV1 infection and Alzheimer's is that, as our immune systems weaken with age, the oral herpes virus is able to travel to the brain. Another piece of the puzzle is a version of a gene known as APOE, which plays a role in the manufacture of lipoproteins. It appears that the herpes virus either reactivates more frequently in people who are carriers of that particular gene variant, or that the reactivation is more harmful. Either way, the result is believed to cause changes within the brain tissue that lead to Alzheimer's.

Considering how many of us get cold sores, these new developments can be unnerving. That's why it's important to note that these findings are still preliminary, and more research is needed. The very good news is that, should the HSV1 theory prove to be correct, it gives scientists their first real line of attack against Alzheimer's disease, in the form of antiviral drugs. It even opens the door to the development of an anti-Alzheimer's vaccine.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I recently read that more than 30 students at a school in North Carolina all got chickenpox during an outbreak. Growing up, I got chickenpox, too, before there was a vaccine. Is the vaccine really that necessary for kids? Like I said, I got chickenpox as a kid and turned out fine!

Dear Reader: It's true that most children who develop chickenpox, a highly contagious disease caused by the varicella-zoster virus, go on to make a full recovery. Most often the virus causes an itchy rash that is often accompanied by a fever, headache, and some aches and pains.

However, that's not the whole story. First, it's important to note that from 2 to 6 percent of children who become infected with the chickenpox virus go on to develop complications as a result of the illness, some of them serious. These include pneumonia, bacterial infections, infections of the brain or the blood, and can lead to death. It's when you look beyond the individual consequences and consider the community that chickenpox becomes a health threat far more widespread than an individual child stuck at home for a few weeks with a rash and a fever.

Those at risk of grave complications from a case of the chickenpox include infants under 12 months old, who are too young to receive the vaccine and whose immune systems are not yet fully developed. The same goes for the elderly, whose immune systems become less robust as they age. Also at risk are people whose immune systems are compromised, such as someone undergoing cancer treatment or someone who is HIV-positive.

For a pregnant woman, a case of chickenpox prior to her 20th week can result in health complications for her unborn baby, including scars, eye problems, malformed limbs, poor growth, small head size and delayed development. When the virus is contracted in the third trimester, there is a chance of problems with the baby's central nervous system. The risk is small -- just 1 to 2 percent -- but with safe and effective vaccines available, it's unnecessary. Again, it's all about caring for one's wider community.

When it comes to prevention, the Centers for Disease Control and Prevention recommends that children get an initial dose of chickenpox vaccine between the ages of 12 and 15 months. This should be followed by a second dose of the vaccine between the ages of 4 and 6 years. For people who are 13 or older and have either never been vaccinated, or have never had chickenpox, the recommendation is two doses of the vaccine, given a minimum of 28 days apart. It's true that, despite receiving the vaccine, some people do go on to contract the disease. When that happens, symptoms are usually milder, meaning there are fewer blisters and often no fever. The illness will also typically be of shorter duration.

Most insurance plans will cover the chickenpox vaccine. If not, the Vaccines for Children Program offers help to individuals who qualify. For more information on this program, go to cdc.gov/features/vfcprogram.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)