Dear Doctors: My husband and I both work in an office, and our three kids are in school. That’s a lot of exposure to germs and bugs. When someone gets sick, how do you know if it’s a cold or the flu -- or worse? Do you always need to see a doctor?

Dear Reader: A variety of viruses, bacteria and even fungi can cause respiratory tract infections. Because they affect the same tissues, they often produce similar symptoms. That can make it difficult to know which illness someone has contracted.

The most common respiratory infections here in the United States are two that you’re asking about, namely the flu, or influenza, and the common cold. Other possibilities include COVID-19, pneumonia and bronchitis. Unlike during the height of the pandemic, the flu is outpacing COVID-19 this year. Pneumonia, another possible respiratory infection, is not as common as the flu or a cold. (We are addressing COVID-19 and pneumonia in upcoming columns. Our recent column about bronchitis can be found in the archives.)

The common cold is caused by a virus, usually rhinovirus and sometimes coronavirus. An identifying characteristic of a plain old cold is that the symptoms it causes occur from the neck up. These include a sore throat, clogged sinuses, a runny nose, sneezing, the production of thick (and seemingly endless) mucus, ear congestion, watery eyes and sometimes a headache. Mild chest congestion and a mild fever are possible, but do not always occur.

Having a cold can be miserable, but it rarely needs medical intervention. One notable exception is if it generates an ear infection. This can occur if bacteria begin to grow in fluid that has built up in the middle ear. Symptoms of an ear infection include pain, muffled hearing, visible discharge and dizziness. If symptoms persist or become severe, it can become necessary to see a doctor for antibiotics to clear up the infection.

That brings us to the flu, which is caused by the influenza virus. Unlike a cold, which typically has a gradual onset, the flu hits hard and fast. Symptoms can be similar to those of the common cold, but are markedly more intense. People with the flu often have a high fever; chills, exhaustion and widespread body aches are common. The infection can also affect the respiratory tract, causing a persistent cough and mucus production.

For both a cold and the flu, recovery begins with rest and supportive care. The symptoms are caused by your immune system’s fight against the viral invaders, so you want to help it along. That means drinking plenty of fluids, eating a healthy diet and -- yes, we’re repeating ourselves here -- getting plenty of rest. Over-the-counter medications to address fever, cough, sore throat and congestion can be helpful. Most people will begin to recover in three to five days. For those with influenza, the antiviral medication Tamiflu is an option.

Many people ride out these illnesses at home. But if symptoms become severe, consider an office visit with your doctor for evaluation, diagnosis and further treatment.

(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: I meet up with friends a few days a week to go running. One of them always skips the cooldown and hops right into his car to drive to work. A trainer once told me that’s a recipe for sudden cardiac death. Do you know if that’s a myth, or is there something to it?

Dear Reader: The term “sudden cardiac death” is used to describe a medical emergency that, because it compromises the cardiovascular system, results in the person’s death within an hour of the onset of symptoms. Most often the problems directly involve the heart. These include various types of heart arrhythmias, cardiac arrest, heart attack, cardiomyopathy or stroke. Although not as common, sudden cardiac death can occur due to a drug overdose, trauma or poisoning. Sometimes a cause for the sudden cardiac death cannot be determined. The death occurs because something has caused the heart to stop altogether, or to function so poorly that it was unable to deliver enough blood throughout the body to sustain life.

The most common factor in sudden cardiac death is the presence of coronary artery disease, or CAD. This is a condition in which the interior walls of the arteries that deliver blood to the heart grow narrow, or become completely blocked, due to a buildup of plaque. In younger adults, a heart arrhythmia, such as ventricular or atrial fibrillation, or ventricular tachycardia, is often the cause. These are conditions in which the electrical signals that coordinate the heartbeat go awry, which swiftly disrupts the flow of blood throughout the body.

The good news is that sudden cardiac death during or after exercise is rare. However, the trainer you spoke with is on the right track in discussing the importance of a cooling down period after exercise. When you exert yourself in any way, your heart begins to beat faster and more forcefully in order to deliver the additional oxygen and nutrients needed by the muscles. This, in turn, leads to an increase in systolic blood pressure, which is the force of the blood on the walls of the vessels during a heartbeat. Both the added demands on the heart and the increase in systolic blood pressure will persist for as long as you maintain the pace and intensity of the exercise you are doing.

A cooldown period immediately following prolonged vigorous exercise is beneficial to the heart. It lets you slowly reduce the demands you have been making on your muscles, and thus on your heart. As the muscles work less, their need for oxygen decreases. This allows a return to a slower and less vigorous heartbeat, which in turn begins to ease systolic blood pressure. A cooldown doesn’t have to be elaborate or prolonged. Simply taking the time to slow the pace of your run, to jog for a bit as you regain your breath and then wind down to a few minutes of brisk walking should be enough for both the heart and your blood pressure to have a safe and gradual recovery.

(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: My sister has been diagnosed with myasthenia gravis. It started last year, when she turned 38, and it has been getting worse. I would like to know more about the condition. Also, I have heard that a study says the gut microbiome is involved. Can you please talk about that?

Dear Reader: Myasthenia gravis, also known as MG, is a somewhat rare autoimmune disorder. It occurs when the immune system mistakenly attacks compounds produced by the body that are integral to allowing muscle fibers to contract. MG disrupts the communication pathways between the skeletal muscles and the nerves that animate them. This causes weakness in those muscles, along with fatigue, each of which can intensify throughout the day. MG can occur at any age, but it becomes more common among women at about age 40 and in men after about age 60.

The condition often begins with progressive weakness in the muscles around the eyes. This is known as ocular myasthenia gravis. One or both eyelids may begin to droop, it can become difficult to keep the eyelids open, and the person may experience blurred or double vision. About half of cases of ocular MG progress to include the muscles of the legs, hips, arms, face or neck. This is known as generalized myasthenia gravis. It can become difficult to rise from a chair, navigate stairs, raise or use the arms, control facial expressions and chew or swallow. Generalized MG can also affect the muscles that control the diaphragm and those that connect the ribs, which can interfere with breathing.

At this time, there is no cure for myasthenia gravis. Treatment depends on the scope and severity of each person’s symptoms and how quickly the disease is progressing. It can include medications to improve neural activity, corticosteroids to dampen immune system response or immunosuppressant drugs. None of these is completely effective, and each has the potential for side effects. That’s what makes studies like the one you are asking about so important.

A growing body of research continues to find that the gut microbiome and the immune system work together to maintain the health of the body. There is also persuasive evidence that an imbalance in the populations of microorganisms in the gut can contribute to a range of diseases, disorders and conditions. This includes myasthenia gravis.

When scientists in Spain and Italy explored the role of the gut in MG several years ago, they saw intriguing results. They compared fecal samples from 10 adults living with MG with those from 10 adults of the same age and sex who do not have the disorder. All participants lived in the same region. When the researchers analyzed the types and quantities of microorganisms present in the fecal samples, and ran their genetic profiles, they found striking differences between the two groups. Specifically, unusually large populations of certain bacteria were associated with an elevated risk of developing MG. The researchers hope that further research will lead to the development of prebiotics or probiotics that can modulate the microbiota of MG patients and improve, or even eliminate, 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.)