Bacterial Infections and Antibiotics Explained

An infectious disease expert breaks down what causes bacterial infections, when antibiotics are necessary, and how infections can turn into sepsis.

While most bacteria found in the environment and our bodies — such as on the skin and in the gut — are harmless, some can cause infections, including strep throat and urinary tract infection. Recently, Madonna was in the news when she was hospitalized for what her manager called a serious bacterial infection.

Bacteria are not visible to the human eye, but we have about 10 times more bacterial cells in our bodies than we have human cells, estimates the National Human Genome Research Institute. But only less than 1% of different types of bacteria can make people sick with bacterial infections.

Health Matters spoke with Dr. David M. Goldberg, an internal medicine physician at NewYork-Presbyterian Medical Group Westchester, who shared what causes these infections; how they are treated; and potential complications, such as when they lead to sepsis.

Dr. David Goldberg

What causes bacterial infections? What are a few examples?
Dr. Goldberg: Bacteria are single-celled organisms that can reproduce quickly and become infectious. There are many different types of bacterial infections, including pneumonia, which causes the air sacs in your lungs to fill up with fluid or pus; urinary tract infections; and infections of the nervous system, such as meningitis (inflammation of the lining around the brain and spinal cord).

As the names imply, bacterial infections are caused by bacteria, which have the capacity to live on their own, while viral infections are caused by viruses, which are pieces of RNA or DNA wrapped in a coat. Unlike bacteria, viruses cannot live independently. They have to live inside another cell.

How are bacterial infections treated? How does treatment work?
Bacterial infections can be treated with antibiotics. Think of the healing process from a bacterial infection as a tug of war between the bacteria and our immune system. The antibiotics add one extra player to our side, and that can help pull someone over the line. But it is not the antibiotics doing it by themselves. It is a battle between the bacteria and the immune system. Antibiotics give us a hand by killing the bacteria or slowing their growth.

There are two kinds of antibiotics: bactericidal and bacteriostatic. Bactericidal antibiotics kill the bacteria, while ones that are bacteriostatic make the bacteria static (slows their growth). Static antibiotics can work perfectly well — simply suppressing the bacteria from growing is enough because we have an immune system.

It’s important to note that antibiotics do not work on viral infections, like COVID-19 or the flu.

At what point does a doctor prescribe an antibiotic? Are they effective?
The first questions are, what kind of bacterial infection is it, and how serious is the infection? Some cases can resolve without treatment, but others may need to be treated with antibiotics.

Urinary tract infections tend to get better on their own, especially in healthy young people, by simply drinking lots of fluids. But other bacterial infections need to be treated to prevent complications. For example, if left untreated, strep throat can lead to rheumatic fever, a condition that causes inflammation in the heart, blood vessels, and joints.

Another scenario is pelvic inflammatory disease, an infection of the female reproductive organs, usually caused by sexually transmitted organisms such as chlamydia and gonorrhea. Pelvic inflammatory disease should be treated with antibiotics, even if mild, since the infection may lead to infertility.

Antibiotics are effective, but there are things to keep in mind. For certain vulnerable populations, like people who have weak immune systems or have other comorbidities, such as cancer, even if they are given the right antibiotics, they may not recover.

And in general, some bacteria have become resistant to antibiotics.

What is Antibiotic Resistance?

According to the Centers for Disease Control and Prevention (CDC), antibiotic resistance occurs when bacteria or fungi no longer respond to the drugs that were made to remove them, meaning that they continue to grow. In the U.S., about 2.8 million people have bacterial infections that are resistant, resulting in more than 35,000 deaths.

“As we give more antibiotics, the bacteria become more resistant,” says Dr. Goldberg, who is also an assistant professor of medicine at Columbia University Vagelos College of Physicians and Surgeons. “The bacteria learn to avoid effects of the antibiotics. It’s a race that we might lose in the long run unless we are more careful about how often we prescribe and use antibiotics.”

The CDC estimates that about 47 million antibiotic prescriptions are written for infections that do not need antibiotics, such as viral infections.

For bacterial infections, Dr. Goldberg says that before he prescribes antibiotics he discusses the severity of the infection with the patient, goes over their health history, and addresses the side effects of the antibiotics. “These are reasons that can help a doctor decipher whether or not to prescribe and reasons that can help a patient know if they should take antibiotics,” he says.

What are the side effects of antibiotics?
There can be many side effects. The most important probably is an allergic reaction. People can swell up and have trouble breathing. There are also milder side effects, such as diarrhea, nausea, and a rash.

There’s quite a large number of antibiotics. And that is good news. Back in the 1940s, all we had was penicillin. And now we have many types (or classes of antibiotics). Even if you are allergic to one class of antibiotics or even two or three, there is almost always another antibiotic that you can get.

Are antibiotics administered differently, depending on the case?
It is usually oral, but every now and then there is an infection that needs to be treated with intravenous antibiotics. In most cases, the blood levels of antibiotics are much higher if given intravenously than if given orally, since the antibiotic may not be fully absorbed when given by mouth. If someone is seriously ill, and we want to make sure they have high levels of antibiotics, or if someone is unable to take oral antibiotics because of vomiting or some other reason, we give it to them intravenously.

But even if administered intravenously, a patient does not have to be admitted to the hospital. If it is once a day, for example, an intravenous catheter is placed in the patient’s arm, and they are given a dose of the antibiotic once a day in an outpatient setting.

Sometimes you can give an antibiotic topically, meaning by a cream, especially for certain skin infections. Occasionally, antibiotics are given as a nebulizer, as inherent to the lungs or the nose; that is much less common.

What are sepsis and septic shock? Can bacterial infections lead to these conditions?
Sepsis is a serious reaction to infection that is life-threatening and requires immediate care in a hospital. About 1.7 million adults in the U.S. develop sepsis, and at least 350,000 die during their hospitalization, according to the CDC. In about 87% of cases, sepsis, or the infection that causes sepsis, begins before a person goes to the hospital.

Most of the time, it is caused by bacterial infections, such as a skin infection from a cut or a lung infection like pneumonia, but can also be caused by viral infections. Sepsis causes inflammation across large areas of the body and can damage tissue and multiple organs, such as the heart, brain, lungs, and kidneys. The risk of a bacterial infection leading to sepsis is much higher for infants, older adults, and people who are immunocompromised.

When someone develops sepsis, they may experience breathing problems. When the oxygen levels fall, they often become confused. People with sepsis may also experience symptoms like a fast heartbeat, chills, and low blood pressure, as they have less blood going to the brain.

Septic shock is the most severe stage of sepsis, where the blood pressure drops to dangerously low levels. Even if you give the person fluids, the blood pressure stays low. If in septic shock, a person is taken right to the intensive care unit.

What is the course of treatment at that point? 
If a person arrives at the emergency room, the first question is, what is the source of infection? We get chest X-rays and do blood and urine cultures, among other tests. Usually with sepsis, though not always, the infection is spread to the bloodstream, which is more ominous. You might get a CAT scan of the chest with the abdomen, looking for infection there, depending upon what the person’s symptoms are, what the examination shows.

We do all of that, and then if we think the person might be septic, we administer intravenous antibiotics right away. When given intravenously, we know they are getting a big dose right into the entire body. They are also given intravenous fluids to keep the blood pressure up and oxygen. If the oxygen levels are low — and in severe cases, somebody really can’t breathe for themselves — they are put on a respirator.

What should people keep in mind if they think they may have a bacterial infection?
Most bacterial infections do not lead to sepsis or septic shock. But it is important to assess the severity of a bacterial infection with your doctor — not just how bad it may be now, but the risk of complications. A doctor can help determine the best course of action depending on the source of infection and health of the patient.

David M. Goldberg, M.D., is an internist and infectious disease specialist at NewYork-Presbyterian Medical Group Westchester and assistant professor of medicine at Columbia University Vagelos College of Physicians and Surgeons. He is board-certified in Internal Medicine and Infectious Diseases and has a special interest in travel medicine, Lyme disease, HIV, and community-acquired infections.

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