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Atypical organisms such as Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella pneumophila are implicated in up to 40 percent of cases of community-acquired pneumonia. Antibiotic treatment is empiric and includes coverage for both typical and atypical organisms. Doxycycline, a fluoroquinolone with enhanced activity against Streptococcus pneumoniae, or a macrolide is appropriate for outpatient treatment of immunocompetent adult patients. Hospitalised adults should be treated with cefotaxime or ceftriaxone plus a macrolide, or with a fluoroquinolone alone. The same agents can be used in adult patients in intensive care units, although fluoroquinolone monotherapy is not recommended; ampicillin-sulbactam or piperacillin-tazobactam can be used instead of cefotaxime or ceftriaxone. Outpatient treatment of children two months to five years of age consists of high-dose amoxicillin given for seven to 10 days. A single dose of ceftriaxone can be used in infants when the first dose of antibiotic is likely to be delayed or not absorbed. Older children can be treated with a macrolide. Hospitalised children should be treated with a macrolide plus a beta-lactam inhibitor. In a bioterrorist attack, pulmonary illness may result from the organisms that cause anthrax, plague, or tularaemia. Sudden acute respiratory syndrome begins with a flu-like illness, followed two to seven days later by cough, dyspnoea and, in some instances, acute respiratory distress.