Can Taking Antibiotics Increase Your Chances of Getting an Infection?

Martin Blaser, M.D., is the Director of the Human Microbiome Program and a Past President of the Infectious Diseases Society of America. He asks an important question about our overuse of antibiotics: “Has any health-care professional ever told you that taking antibiotics would increase your susceptibility to infection?”

The utterly counterintuitive answer is “yes,” as Dr. Martin Blaser, an infectious disease specialist at New York University, tells us in his superb just-released book “Missing Microbes: How the overuse of antibiotics is fueling our modern plagues.”

First, some quick background. Dr. Blaser’s concern is with the huge overprescription of antibiotics. In 2010, 258 million courses of antibiotics were prescribed in the United States – that’s 833 prescriptions for every 1,000 people. What Blaser and others such as the U.S. Centers for Disease Control contend is that far too many of these prescriptions aren’t necessary. For example, only 20% of upper respiratory tract infections are caused by bacteria. Yet patients demand and doctors routinely prescribe antibiotics for sore throats, runny noses, chest colds, pneumonia’s, and so on, without first checking to see if the cause is viral or bacterial.

So what happens then, if you take an antibiotic when you shouldn’t? Or perhaps worse, what happens if you have simply taken too many courses of antibiotics over the years? The answer in both cases is that you make yourself more susceptible to infections.

Dr. Blaser offers us 3 pieces of evidence to explain this unintended consequence of antibiotic use.

As usual we begin with our animal friends, the mice. Researchers fed normal mice a species of Salmonella that causes disease in them and us. Although infection occurred, it took 100,000 Salmonella organisms injected into a mouse to infect half the population.

But the researchers wanted to know what would happen if you first gave the mice an antibiotic, in this case streptomycin. Since antibiotics kill bacteria, the mice should be immune. But that’s not what happened. Instead they found that it now took only 3 Salmonella organisms – not 100,000 – to infect half the mouse population: that’s a thirty thousand-fold difference.

Subsequent research substituting Staphylococcus bacteria and penicillin for Salmonella and streptomycin showed the same results: i.e. taking an antibiotic before being exposed to a germ greatly increases your risk of infection.

Next up is the Chicago Salmonella outbreak of 1985 where at least 160,000 people became ill and several died. Scientists tracked down the origin of the Salmonella to contaminated milk from a single grocery store chain. The health department asked people who became sick a simple question: Have you received any antibiotics in the month prior to becoming ill? They found that those who had taken antibiotics got sick at a rate five and half times greater than those who hadn’t taken antibiotics. So just like with the mice, the taking of antibiotics before being exposed to a germ increased your risk of that germ making you sick.

Then, in 2001, researchers wanted to know whether people who received a one week regime of antibiotics would exhibit an increase in the quantity of their bacterium Staphylococcus epidermidis, which is naturally found on your skin. The result: subjects given an antibiotic had a “dramatic” increase in the Staph skin bacteria; whereas the “controls,” the people not treated with antibiotics, showed no increase in their Staph count. What’s more, the increased amount of Staph remained on the skin for 4 years, which is when the experiment ended. So we don’t know how much longer the organism would have persisted.

So how do we account for the result in these 3 cases – the mice, the milk, and the skin Staph – where taking an antibiotic before being exposed to a germ actually increases your chance of that germ making you ill? It’s that seemingly innocuous phrase in paragraph 5 above: “Since antibiotics kill bacteria.” Antibiotics kill ALL bacteria, the “good” and the “bad.” Good bacteria operate in conjunction with your immune system to protect you from disease. So if you knock them out with an antibiotic and are then exposed to a disease-causing germ, your chances of that germ making you sick go up – way up.

One more thing. That alarm sounding mouse experiment that showed a thirty thousand-fold reduction in the number of germs it took to infect you after being inoculated with an antibiotic – – it was done in 1954. But at that time the study came as an inconvenient truth. That’s because antibiotics had only been available for 10 years and they had just served a noble purpose in World War 2, warding off countless infections in soldiers due to battlefield wounds. So antibiotics were a good thing and we didn’t want to hear anything different.

But now, some 60 years later Dr. Blaser says it’s past time that we confront this inconvenient truth. As he puts it: How many doctors ever tell you that antibiotic use can increase your risk of infection?

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4 Responses to “Can Taking Antibiotics Increase Your Chances of Getting an Infection?”

  1. […] Tuesday’s blog we addressed the emerging topic of how antibiotics leave you more vulnerable to infection. The reason is that antibiotics work more like a shotgun than a target rifle: they kill all […]

  2. […] not just cancerous ones. So instead of being left, say, bald, weak, thin, and nauseous, we are left more prone to infection, obesity, childhood diabetes, food allergies, celiac disease, and even […]

  3. […] fact, as we’ve previously reported, your risk of future infection goes way up. That’s according to the work of infectious […]

  4. […] healthy immune function accounts for perhaps the most surprising ill effect of antibiotics of all: an increased risk for infection. That’s the conclusion of infectious disease specialist Martin Blaser, MD, of the NYU School of […]

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