As the second wave of H1N1 infections begins in the United States, federal, state, and local health authorities nationwide are scrambling to prepare for the strains on emergency medical systems. In response, officials across the country are rewriting disaster plans and stocking up on masks, gowns, drugs, and other supplies. One key line of attack will be encouraging people who are not really sick or are suffering only mild symptoms to recover at home. And experts are searching for ways to help healthcare providers quickly screen those who do seek help and separate bad cases from less-severe ones.