This study, conducted over four consecutive winters, aimed to evaluate the epidemiology and clinical effects of respiratory syncytial virus (RSV) infection in elderly and high-risk adults. The study included prospective cohorts of healthy elderly patients (≥65 years) and high-risk adults (with chronic heart or lung disease), as well as hospitalized patients with acute cardiopulmonary conditions. RSV and influenza A infections were diagnosed using culture, reverse-transcriptase polymerase chain reaction (RT-PCR), and serologic studies. Key findings include: - RSV infection was identified in 102 patients in the prospective cohorts and 142 hospitalized patients, with an annual incidence of 3-7% in healthy elderly patients and 4-10% in high-risk adults. - RSV infection was more common than influenza A in the high-risk group but less common in the healthy elderly group. - In both groups, RSV infection led to similar lengths of stay, rates of intensive care use, and mortality. - RSV infection accounted for a significant proportion of hospitalizations for pneumonia, chronic obstructive pulmonary disease, congestive heart failure, and asthma. - The study highlights the importance of RSV infection in elderly and high-risk adults, emphasizing the need for an effective RSV vaccine to reduce the disease burden. The study underscores the need for better awareness among internists about RSV and the importance of yearly influenza vaccination programs, particularly in high-risk populations.This study, conducted over four consecutive winters, aimed to evaluate the epidemiology and clinical effects of respiratory syncytial virus (RSV) infection in elderly and high-risk adults. The study included prospective cohorts of healthy elderly patients (≥65 years) and high-risk adults (with chronic heart or lung disease), as well as hospitalized patients with acute cardiopulmonary conditions. RSV and influenza A infections were diagnosed using culture, reverse-transcriptase polymerase chain reaction (RT-PCR), and serologic studies. Key findings include: - RSV infection was identified in 102 patients in the prospective cohorts and 142 hospitalized patients, with an annual incidence of 3-7% in healthy elderly patients and 4-10% in high-risk adults. - RSV infection was more common than influenza A in the high-risk group but less common in the healthy elderly group. - In both groups, RSV infection led to similar lengths of stay, rates of intensive care use, and mortality. - RSV infection accounted for a significant proportion of hospitalizations for pneumonia, chronic obstructive pulmonary disease, congestive heart failure, and asthma. - The study highlights the importance of RSV infection in elderly and high-risk adults, emphasizing the need for an effective RSV vaccine to reduce the disease burden. The study underscores the need for better awareness among internists about RSV and the importance of yearly influenza vaccination programs, particularly in high-risk populations.