Abstract
BACKGROUND: Respiratory viral infections, including Human Metapneumovirus (HMPV), Influenza (Flu), and human Respiratory Syncytial Virus (hRSV), are major global health concerns. While their impact on vulnerable groups is known, their characteristics in healthy adults (18-65 years) are less clear. This study aimed to determine the incidence and clinical-laboratory features of RSV and HMPV in this population and compared them with those of Influenza A(H1N1) and influenza A(H3N2) for improved epidemiological and diagnostic understanding. METHODOLOGY: A retrospective analysis was conducted on data from an Acute Febrile Illness surveillance (2016-2018) in Manipal, India. The study included 96 HMPV, 68 hRSV, 75 Influenza A(H1N1), and 76 Influenza A(H3N2) positive hospitalized adults with fever (≥ 38 °C) and respiratory illness confirmed by RT‒PCR. Clinical and laboratory data collected within the first 8 days of illness were statistically analyzed. RESULTS: The annual incidence rates of hRSV (0.33%-1.59%) and HMPV (0.14%-1.79%) varied. Coryza was common, but cough was most frequent in HMPV (97.9%). HMPV also resulted in increased rates of shortness of breath and chest pain. Leucopenia was most common in Influenza A(H1N1) patients, and thrombocytopenia was most common in hRSV patients. Significantly elevated leukocyte and platelet counts were observed in HMPV patients. Liver enzyme abnormalities are relatively common in hRSV and Influenza A(H1N1) patients. Symptom progression and laboratory trends revealed distinct patterns across the viruses. CONCLUSION: Despite overlapping initial symptoms, HMPV, hRSV, and influenza resulted in different clinical and laboratory profiles in adults. HMPV was associated with more prominent lower respiratory symptoms and a stronger inflammatory response. These distinctions can aid in the clinical differentiation and management of these common respiratory viruses in adults, highlighting the importance of timely diagnosis for improved patient care and public health strategies.