For reasons that are still unclear, most of the drug-resistant cases have been seen among adults, particularly men who have sex with men, people experiencing homelessness and people with H.I.V. “We’re seeing drug-resistant Shigella infections among these vulnerable populations, and that’s concerning,” said Dr. Naeemah Logan, also a medical officer at the C.D.C. Drug-resistant strains have also been identified in people who recently traveled internationally.
Shigella spreads very easily, with only a tiny amount of the bacteria required to trigger illness. People are exposed when bacteria present in fecal matter come into contact with the nose or mouth. Common routes of transmission are unwashed hands, sexual activity and contaminated food. (Food transmission most often stems from an infected person preparing or serving a meal, not Shigella in the food supply.)
To limit the spread of the bacteria, Dr. Logan urged people to practice good hand hygiene, washing with soap and warm water for at least 20 seconds after using the bathroom or changing diapers, before preparing food, and before and after sex. “Hand-washing hygiene really can’t be dismissed. It’s such a crucial strategy to curb transmission,” she said.
People can remain infectious even after their symptoms have resolved, so Dr. Logan advised that anyone with diarrhea avoid swimming pools and abstain from sex for two weeks afterward.
Why is antibiotic-resistant Shigella suddenly on the rise?
The use of antibiotics is what drives antibiotic resistance in bacteria. The microbes that are susceptible to the medications die off, while the ones that have evolved to evade them will survive and spread.
“The more we use antibiotics, the more bacteria become resistant to them — that’s a kind of inevitable evolutionary process,” Dr. Baker said. “It’s quite common that once it goes on this trajectory, the resistant organisms get selected for, and therefore they take over very quickly within a short space of time.”
Bacteria can acquire drug resistance through random DNA mutations or by swapping genes with other strains or species. Shigella is particularly good at picking up new genes, so antibiotic resistance often emerges in Shigella before it does in other types of bacteria. But DNA sharing goes both ways.
