copyright 2009, The Washington Post WASHINGTON -- Nurses at community clinics are being fitted for respirators. Universities are placing hand sanitizers in dormitory lobbies. Hospitals are preparing to screen and separate patients at emergency rooms. Businesses are setting up phone trees so they can operate with up to a third of their employees out sick. All are signals that swine flu is expected to come roaring back with the cooler weather of autumn. Although the H1N1 strain of the influenza virus has proven to be mild to moderate so far, officials are preparing in case it rebounds more strongly. Urban areas such as the District of Columbia, where about 100 people have been confirmed with the H1N1 virus since spring, face a distinct set of challenges. Crowds, for instance, increase the chance of getting the flu. 'All urban areas are at risk,' said John Williams, vice president for health affairs at George Washington University. 'We're all huddled together -- on Metro, on the bus, in stadiums and theaters. That's a perfect breeding ground.' Residents of most big cities have high rates of asthma, diabetes, HIV and obesity, all of which can increase the severity of symptoms in patients who catch the flu, whether seasonal or H1N1. Several of the diseases, including diabetes and asthma, disproportionately affect minorities. 'There is a lot of poverty-associated illness in major cities,' said James Chamberlain, chief of emergency medicine at Children's National Medical Center. 'Asthma, diabetes, HIV are all more common in cities.' Influenza can exacerbate asthma, particularly in children, because viral infections create mucus that clogs their narrow airways more severely than in adults. In Boston, for example, half of the 71 people hospitalized with swine flu in the spring had asthma. About 11,000 children and 40,000 adults in Washington have asthma, more than 36,000 residents have diabetes, 15,000 have HIV or AIDS, and more than 11,000 have heart disease, according to Department of Health statistics. The children with asthma visit emergency rooms up to five times more than the national average, said Stephen Teach, associate chief of emergency medicine at Children's. 'We don't know how it will unfold,' Teach, a specialist in pediatric asthma, said about swine flu. 'Right now, there's no reason for excessive worry. It's right to be concerned. It's right to plan. It's right to be informed. But it's not a time to be overly concerned until we have a little more data and experience.' People with underlying conditions affecting the lungs or immune system will have priority to receive the swine flu vaccine, along with young people, pregnant women, caregivers and first responders. Nationally, about 159 million people are estimated to be in priority groups. The D.C. Health Department has provided N95 respirators, which filter 95 percent of particulates, to health care workers at primary-care clinics throughout the city, said Beverly Pritchett, head of the emergency preparedness administration. It also has stockpiled thousands of surgical masks and doses of the antiviral medications Tamiflu and Relenza. In a flu outbreak, callers to the 311 government services number seeking information on the flu would be directed to a unit specializing in advice on the flu and the vaccines, which will be available through private physicians and mass vaccination clinics. At Children's National Medical Center, the emergency preparedness committee that does planning for natural disasters and terror attacks has ordered more masks, gloves, hand gel and antiviral medications. Chamberlain said a patient surge in the spring underscored the need to isolate suspected flu patients coming to the emergency room so that vulnerable patients, such as children with cancer, would not be exposed. 'We learned very effective ways to do rapid screening and forwarding of patients in different areas,' he said. 'We expect another surge in the fall. We believe we're prepared.' Primary-care clinics are preparing to notify patients to get vaccinated. 'We're concerned. Our staff is concerned. Our patients are concerned,' said Janelle Goetcheus, medical director of Unity Health Care, which has 81,000 patients, most of them poor or homeless. 'What we've been waiting for is to know when the vaccine is going to arrive so we can get our patients in.' 