Dear Doctors: Our family just spent two weeks passing around a nasty stomach flu. Now that we’re all OK, I realize I don’t know what hit us. Was it the same bug that gives you the regular flu? How does it get from one person to another?

Dear Reader: What we commonly refer to as “stomach flu” is more accurately known as “viral gastroenteritis.” It’s different from the actual flu, which is a respiratory illness that affects the throat, nose and lungs. Unlike the flu, which is caused by the influenza virus, stomach flu typically arises from infection with a different set of viruses. They target the gastrointestinal tract, which includes the stomach and the large and small intestines.

The two most common causes of viral gastroenteritis are rotaviruses and noroviruses. Rotavirus disease is most often seen in infants and young children. Older children and adults can also become infected, but their symptoms tend to be less severe. Noroviruses, which are the most common cause of stomach flu in adults, can affect children as well.

Both rotaviruses and noroviruses are highly contagious. They spread through direct contact with contaminated food, drink, dishes, utensils and surfaces, and through close contact with an infected individual. Both of the viruses are shed in a contaminated person’s stool. If that person fails to thoroughly wash their hands after a bowel movement, they can spread the live virus to everything that they touch.

Symptoms of viral gastroenteritis typically begin 12 to 48 hours after infection. They include stomach discomfort or cramping, feeling nauseated, vomiting, persistent diarrhea, loss of appetite and exhaustion. Some people also have muscle aches, headache or a low-grade fever. Diagnosis is based on someone’s symptoms, plus a physical exam. A stool sample may be used to rule out bacterial or parasitic illness, which can have similar symptoms. A mild case of viral gastroenteritis lasts for two to three days. A more severe infection can persist for a week or more.

One of the risks of this type of illness is becoming dehydrated. This is due to the fluids lost through diarrhea and vomiting, which can be difficult to replace when you’re feeling too nauseated to eat or drink. This is particularly dangerous for the very young and for older adults. It’s important for someone with gastroenteritis to stay hydrated by drinking small amounts of clear fluids throughout the day. Drinking too much, or too quickly, can increase nausea. Younger and older patients may require special oral rehydration fluids. You should seek guidance on these from your health care provider. It’s important to be alert to signs of dehydration. These include dry skin, dry mouth, little or no urine, urine that is a deep yellow color, or feeling faint, dizzy or lightheaded. If these occur, seek medical help immediately.

Since antibiotics don’t work against viruses, treatment focuses on easing the patient’s symptoms. This includes rest, hydration and a bland diet as you gradually ease back into eating. New parents might consider asking their pediatrician about the rotavirus vaccine, which is effective at preventing serious symptoms.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Hello again, dear readers! It’s a busy and, let’s face it, sometimes stressful time of year. We urge you to take a bit of time for yourself to regroup, even if it’s just a bit of deep breathing or a quick walk outdoors. If any of you have coping mechanisms for stress that might be helpful to others, we’d love to hear them. And now, onward to your letters.

-- As booster shots roll out in greater numbers, readers are asking what to expect. “Our son had significant side effects lasting 24 hours after his second Pfizer vaccination,” a reader said. “Is it known what will happen with a third shot of Pfizer?” So far, people who have received booster shots say their reactions are similar to those of the initial two-shot or single-dose series. Fever, headache, fatigue and pain at the injection site are the most commonly reported side effects. Most were mild to moderate and rarely lasted longer than a day or so. At this time, anyone 16 and older is eligible for a booster. For Pfizer and Johnson & Johnson, the booster is the same formulation and dose as the original vaccine; the Moderna booster is the same formulation, but half the original dose.

-- In a recent letters column devoted to COVID-19 questions, we referred to the vaccines as being authorized for emergency use by the Food and Drug Administration. A reader from Spokane, Washington, wondered if we had made an error. “Is the vaccine not, in fact, FDA approved?” she wrote. “That is important, as many are using the emergency-use designation as a reason to not get vaccinated.” The status of the three coronavirus vaccines has been of great interest, and in a bit of flux. All three -- the Pfizer, Moderna and Johnson & Johnson -- started with an emergency-use authorization (EUA) by the FDA. That’s a mechanism that makes rigorously tested medications available before the formal approval process is complete. Our reader is correct that the Pfizer vaccine has received full FDA approval for use in people 16 and over. However, use of the Pfizer vaccine in those younger than 16, and as a booster shot, remains under an EUA. The Moderna and Johnson & Johnson vaccines are both still undergoing the FDA approval process.

-- In response to a column about slow-to-heal bones, a reader suggested that an important part of how bone tissue is formed had been left out of the discussion. Specifically, the calcium-binding actions of magnesium and vitamin K2. While it’s too complex to cover in a letters column, we agree that she makes an excellent point. We will revisit the question in greater depth in an upcoming column soon.

We’ll close by thanking you for taking the time to write. You’ve kept our mailboxes full. We want to keep up with as many of your questions as we can, so we’ll be writing a letters column next week, as well. Meanwhile, please remember that you can find all of our columns online in a searchable database at uexpress.com/health/ask-the-doctors.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: We live in Northern California, and every time we have high winds, the electric company shuts off power because of the fire danger. We use candles and lanterns to light the house, and my husband thinks that he sleeps better on those nights. Do you think there’s a connection?

Dear Reader: We humans, like most creatures on this planet, are keyed to the daily cycle of light and dark. It’s reflected not only in our habits and behaviors, but research shows that it plays out at the cellular -- and even the molecular -- level, as well. Known as the circadian cycle, and often referred to as the body clock, it guides metabolic and biological processes throughout our bodies. A number of these, including the regulation of body temperature, hormone secretion and alertness, play key roles in preparing the body to switch from wakefulness to sleep.

Studies have shown that exposure to even small amounts of artificial light can delay the body’s important sleep prep. It means that with the very first campfire humans lit to push back the night, they disrupted the sensitive mechanisms of the circadian cycle. As firelight gave way to candlelight, then to gas light and now to electric light, that disturbance grew progressively more pronounced. That’s because, as we now know, spending time in bright light slows production of melatonin, which is the hormone whose nighttime spike helps make us sleepy. The advent of blue light in all of the screens we use has also been shown to wreak havoc on sleep quantity and sleep quality.

In a small study conducted by researchers at the University of Colorado at Boulder, eight participants camped in a wilderness area so remote, it was free of any artificial light. The campers left all portable light sources behind and lived solely by natural daylight. Lab tests showed that after only a week, their daily melatonin rhythms, as well as their individual sleep schedules, were syncing to the daily ebb and flow of light. The takeaway was that, due to reduced exposure to sunlight in our largely indoor lives, and the near-constant presence of electric lights, human circadian physiology has been altered.

Interestingly, another study found a wide range in tolerance to artificial light. For some participants, the dim glow of just a few candles caused the same drop and delay in melatonin production that others in the study experienced only in the presence of sustained bright light. All of which adds up to the fact that yes, it’s entirely possible your husband’s sleep improves when his days and evenings are free from screens and electric lights. This is important because insufficient sleep and low-quality sleep are linked to a number of serious health conditions. These include high blood pressure, depression, obesity and coronary heart disease. The sleep deficit in the United States is so severe, the Centers for Disease Control and Prevention has flagged it as a public health problem.

You don’t need to go cold turkey on electrical light. But the research is clear: Spending more time in daylight and dimming the lights -- and screens -- after dark can add up to better sleep.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)