March 27, 2012 -- intro: As bacteria evolve to evade antibiotics, infections that were once easily cured could become deadly. According to Dr. Margaret Chan, director general of the World Health Organization, "things as common as strep throat or a child's scratched knee could once again kill."
"We are losing our first-line antimicrobials," Chan said March 14 in her keynote address at the conference on combating antimicrobial resistance. "Replacement treatments are more costly, more toxic, need much longer durations of treatment, and may require treatment in intensive care units."
Once thought to be relegated to hospitals and nursing homes, antibiotic resistant bacteria are invading communities worldwide. ABC News asked infectious disease experts which superbugs pose the biggest threats.
quicklist: 1category: Top 5 Risky Superbugstitle: The Original Superbug: Staphylococcus Aureusurl:text: Almost everyone's heard of MRSA, or methicillin-resistant Staphylococcus aureus. But few people understand just how pervasive the original superbug has become.
Roughly one in 50 people carries a strain of staph resistant to common antibiotics, according to the National Institutes of Health. If the bug invades a wound, it can cause an infection that's minor and localized, as in a pimple, or serious and widespread, involving the heart, lungs, blood and bones.
"MRSA continues to be the biggest threat because it could become more widespread," said Dr. William Schaffner, chair of prevention at Vanderbilt University Medical Center.
MRSA infections usually strike elderly hospital inpatients or nursing home residents. But the number of MRSA cases out in the community is on the rise, according to the NIH. It can spread between people working out at the gym through contaminated towels or equipment, and has even been passed between children at day care facilities.
quicklist: 2category: Top 5 Risky Superbugstitle: The Hospital Lurkers: Clostridium Difficile and Acinetobacterurl:text: Doctors have long been battling a group of six hospital-borne pathogens dubbed ESKAPE: Enterococcus, Staphylococcus, Klebsiella, Acinetobacter, Pseudomonas and Enterobacter. Now those six bugs are escaping antibiotics.
"These organisms were present in hospitals 20 years ago," said Dr. John Bartlett, chief of infectious diseases at Johns Hopkins University School of Medicine in Baltimore. "Now we've used so many antibiotics to treat them, they've been trained to become resistant."
The bacteria invade vulnerable bodies through hospital equipment, like surgical implants and central lines.
"When people come into the hospital, they often get metal put in them, or plastic lines. All of those foreign bodies become susceptible to infection," said Bartlett. "We can't help it. It's nobody's fault."
quicklist: 3category: Top 5 Risky Superbugstitle: The Food Borne Bugs: Escherichia Coli and Salmonellaurl:text: The bacteria behind food poisoning are becoming drug resistant, partly because farm animals are fed antibiotics to promote growth.
"Eighty percent of antibiotics in the U.S. are given to animals, not people," said Bartlett. "Now we're tracing some of these antibiotic resistant infections back to the farm."
Earlier this month, the U.S. Centers for Disease Control and Prevention reported that drug-resistant strains of E. coli causing urinary tract infections in women could be traced back to chickens fed antibiotics.
"E. coli is the most common cause of simple urinary tract infections, which we can very quickly and easily today. But as it becomes resistant, what was once simple [to treat] will become complicated," said Schaffner.
The European Union has banned antibiotics as growth-promoters. But the U.S. continues to lag behind, only recently restricting the use of antibiotics called cephalosporins in livestock.
"Quite frankly, I think that's embarrassing," said Bartlett. "Nobody's talking about the U.S. being very aggressive or successful in dealing with this problem."
A federal court judge ruled Thursday that the U.S. government must take steps to ban the use of penicillin and tetracycline -- antibiotics used to treat pneumonia, strep throat and urinary tract infections in humans -- in animals.
quicklist: 4category: Top 5 Risky Superbugstitle: The Sexually-Transmitted Infections: Gonorrhea and Chlamydiaurl:text: Super gonorrhea may sound funny, but it's no joke. Antibiotic resistance means sexually-transmitted infections once cured with a few pills could require treatments that are more invasive.
"We might have to rely on intravenous or intramuscular treatments, meaning the patient would have to come in or someone would have to go to their home," said Schaffner. "These people don't want to be recognized in their home environment as having one of these infections, which a visit would kind of announce. So people will begin avoiding treatment. You have a spiraling series of problems."
quicklist: 5category: Top 5 Risky Superbugstitle: The Global Threat: Tuberculosisurl:text: Tuberculosis kills 1.34 million people each year worldwide. And now the disease, once curable with antibiotics, is becoming resistant to multiple drugs.
"Among the world's 12 million cases of tuberculosis in 2010, WHO estimates that 650,000 involved multidrug-resistant TB strains," WHO's Chan said in her keynote address. Chan added that treating multidrug-resistant TB is extremely complicated, "typically requiring two years of medication with toxic and expensive medicines, some of which are in constant short supply. Even with the best of care, only slightly more than 50 percent of these patients will be cured," she said.
Although most cases of multidrug resistant TB are in developing countries, there were 92 U.S. cases reported in 2011, according to WHO data.
"We live in a very small world today," said Schaffner, explaining how travelers can import antibiotic resistant bacteria from developing countries. "It's a very small word and the bacteria do not need passports."