Selective losses of human-associated microorganisms may be responsible for a wide range of modern ailments, including esophageal diseases, obesity, asthma, and the epidemic spread of high-grade pathogens, according to Martin Blaser from New York University Langone Medical Center in New York City.
In two to three generations, humans moved from near-ubiquitous colonization by H. pylori-more than 80% of people carried them-to rates in the single digits for children born in the United States and Western Europe, Blaser says. "This is an unprecedented change in human microecology," and reflects more sweeping alterations across the human microbiota, according to Blaser and Stanley Falkow from the Stanford University School of Medicine in Stanford, Calif. They attribute this to multiple factors, including cleaner water, smaller families, births involving a higher percentage of Caesarean sections, a reduced frequency in breastfeeding, and the widespread use of antibiotics, especially among pregnant women and children. Details appear in the December 2009 Nature Reviews Microbiology (doi: 10.1038/nrmicro2245).