Dear Doctor: Like practically everyone else in the United States, we threw out our romaine lettuce because of the E. coli outbreak. What is E. coli and how do we avoid it?

Dear Reader: E. coli is a type of bacteria that lives in the intestines of humans and some animals. It exits the body in feces and can survive outside of the intestines for several hours. Most strains of E. coli (Escherichia coli, for our fellow science nerds) are harmless. In fact, they're a natural part of our gut microbiome. The "good" E. coli perform helpful functions, like the synthesis of certain vitamins and keeping certain pathogens from colonizing the colon.

However, a few strains of E. coli cause disease, including gastroenteritis, which is what we're seeing with the present outbreak. And the potential dangers of the "bad" versions of E. coli don't end there. Pathogenic strains can cause illnesses outside of the gastrointestinal tract, including respiratory illness, pneumonia, urinary tract infections and neonatal meningitis.

When it comes to the current outbreak, laboratory tests show that the strain involved, identified as E. coli O157:H7, produces a particularly nasty toxin; in fact, the hospitalization rate has been higher than in previous outbreaks. As you noted in your question, this outbreak centers around romaine lettuce, which has been contaminated with fecal material containing the pathogenic E. coli.

Infection with E. coli begins anywhere from two to five days after exposure. The first symptoms are abdominal pain, cramping and tenderness, which within 24 hours are followed by diarrhea. As the infection progresses, the diarrhea becomes increasingly watery and -- this can be the scary part -- visibly bloody. That's because the toxin in this particular strain damages the lining of the small intestine. Nausea and headache may accompany the diarrhea, and some people may experience chills and fever. The disease typically runs its course in a week or so. However, in some vulnerable populations, such as young children, older adults and those with weakened immune systems, something called hemolytic uremic syndrome, which is a type of kidney failure, can occur.

The federal Centers for Disease Control and Prevention has warned consumers against romaine lettuce grown in the Yuma, Arizona, region. Unless you know specifically where the romaine lettuce in your fridge originated, it is safest to throw it away. This includes whole heads, hearts, pre-packaged lettuce mixes and premade salads. These same precautions apply to romaine served in restaurant.

In general, the best precaution against infection with E. coli is good hand hygiene. Always wash hands after using the bathroom, changing a diaper or helping someone else use the toilet. Wash hands before handling and preparing food, and after contact with animals.

Always wash fruit and vegetables thoroughly under running water; cook meats to their recommended internal temperatures; and be careful about cross-contamination in the kitchen. Anything that has come into contact with raw meat -- whether it's your hands, countertops, knives, cutting boards or utensils -- is a potential source of disease-causing E. coli.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: Last year, for four months, I smelled cigarette smoke all the time -- even though I wasn't near smokers. The problem went away, but now it's back. I can be in bed, in my kitchen, at the grocery store, even church. I have been diagnosed with benign paroxysmal positional vertigo. Is there a connection? If not, what's causing this?

Dear Reader: I can only imagine what a nuisance this is. The condition is called phantosmia, meaning the smelling of an odor that isn't actually there. Rest assured, you're not alone.

One survey of 3,603 people over the age of 40 found that 6 percent of people experience phantom odors. Another study, of 2,569 people ages 60 to 90, found that 4.9 percent reported phantosmia. The condition is more often reported by women than men, with many women having had a prior short-lived episode between the ages of 15 and 30. For the majority, the phantom odors are unpleasant, often described as the smell of something burned, spoiled, rotten or foul. Thus, the smell of cigarette smoke is not unusual. Symptoms can last from two minutes to 30 minutes at a time; fortunately, they're rarely chronic.

Phantosmia can have a variety of causes, some of them serious. The most common one is inflammation within the nasal cavity or within the sinuses. This is most likely in people who have chronic allergies or recurrent sinus infections, but the condition can also occur with nasal passage inflammation not related to allergies, such as that linked to exposure to solvents, ammonia, benzene, cigarette smoke and drugs inhaled through the nose.

Your diagnosis of benign paroxysmal positional vertigo could theoretically be linked to the condition in that this type of vertigo can be related to middle ear and Eustachian tube dysfunction, which in turn can be affected by nasal and sinus problems. Knowing whether you have a history of nasal congestion or sinus problems might shed light on this potential connection.

Trauma to the nose or the sinuses can also lead to phantosmia, as can head trauma that damages the areas of the brain that process smell. Speaking of the brain, the olfactory bulb located above the nasal cavity is full of nerves that send information about smell to the brain and, as we get older, this area can become damaged and lose many of its nerve cells. This loss can be especially significant in people with neurodegenerative diseases such as Alzheimer's, Parkinson's and Lewy Body dementia, all of which affect the olfactory bulb.

Blood pressure medications, such as beta blockers, calcium channel blockers and ACE inhibitors, can occasionally be linked to both loss of smell and phantosmia. Other potential causes include tumors within the brain or nasal cavity, as well as seizures.

Often, however, no cause can be found. This is termed idiopathic phantosmia and, on the plus side, it improves with time. In fact, 53 percent of patients have improvement or resolution of phantom smells after one year.

So, be encouraged that your symptoms could improve. In the meantime, try nasal rinses -- which could decrease the sense of phantom smells -- and work with your physician to identify, if possible, a cause for the problem.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I hate dieting and have been putting off losing these last 12 pounds of baby weight. My husband says I should at least start exercising because it makes your fat healthier. Can this really be true?

Dear Reader: For all the bad press the fat within our bodies receives, it's actually a vital resource. With more than double the calories per gram than proteins or carbohydrates, it's an efficient system for storing energy that helped our ancient (and not-so-ancient) ancestors survive uncertain times. And while we tend to think of body fat in terms of its physical manifestation, as in the bulge of a waistline, it's actually a dynamic nutrient with multiple forms and functions within our bodies.

In addition to being an energy source, fat helps to manage temperature, cushion vital organs, regulate hormone production, build cell membranes and stockpile certain vitamins. It plays an important role in immune function and brain chemistry, as well as many other metabolic processes. Of course, too much stored fat is problematic, and can lead to adverse health consequences, including diabetes, heart disease and metabolic syndrome, to name just a few.

The complex cycle of how the various fats within our bodies are formed, stored, mobilized and metabolized is still not completely understood. (It's only a decade ago that we learned about the existence of "brown fat," which are fat cells within our bodies that burn rather than store lipids.) Now the results of recent studies have shed light on another question that has long puzzled scientists. That is, why do some overweight individuals develop insulin resistance, which is often a precursor to diabetes, and others do not?

One of the problems with stored fat is that it tends to release fatty acids into systemic circulation. This leads to inflammation, which is a common denominator in developing insulin resistance. But it turns out that not everyone who is overweight or obese has the same degree of release of fatty acids. A study last year from researchers at the University of Michigan found that certain individuals, despite being obese, have low rates of fatty acid release, few markers for inflammation and therefore do not develop insulin resistance. But why?

In a second study, the Michigan researchers looked at whether exercise might play a role. When they compared a group of overweight individuals who exercise regularly with a similar group of overweight individuals who did not exercise, they found that the subcutaneous fat of the active group contained more blood vessels. The two groups then took part in a session of aerobic exercise. Post-exercise biopsies of subcutaneous fat revealed that, after that single session, the stored fat in both groups became less "leaky," and this was considered healthier.

While it's important to note that these were both small studies, the results are intriguing. They add to what we already know about the health benefits of exercise and suggest some interesting directions for future study. In the meantime, we agree with your husband that no matter what you're doing with your diet, adding an exercise component to your daily life is a good idea.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)