A Study of Rilematovir (JNJ-53718678) in Adult Outpatients With Respiratory Syncytial Virus (RSV) Infection

- Presented to the healthcare facility with symptoms suggestive of a diagnosis of acute respiratory syncytial virus (RSV) infection

- Has at least 2 symptoms of lower respiratory tract disease (LRTD), one of which must be scored as at least 'moderate' if the symptoms did not pre-exist before RSV onset, or one of which is scored worse than usual if the symptoms pre-existed

- Tested positive for RSV infection using a molecular-based diagnostic assay (polymerase chain reaction [PCR] or other) on a bilateral nasal mid-turbinate swab sample

- Has at least one of the following high-risk conditions that predispose them to RSV-related disease progression: a. age greater than or equal to (>=) 65 years, b. congestive heart failure (CHF), c. chronic obstructive pulmonary disease (COPD), d. asthma

- Randomized to study intervention treatment within 72 hours after onset of any of the RSV symptoms or worsening of pre-existing symptoms

- Not be hospitalized during screening (emergency room or hospital observation status for an anticipated duration of less than [<] 24 hours are not considered as hospitalization)

- Known allergies, hypersensitivity, or intolerance to rilematovir or to any of the excipients of rilematovir or placebo formulation

- Presence of clinically significant heart arrhythmias, uncontrolled, unstable atrial arrhythmia, or sustained ventricular arrhythmia

- Participant has known or suspected (from medical history or participant examination) chronic or acute hepatitis B or C infection

- Immunocompromised conditions

- Living in institutional care or assisted living facility and also receiving acute care management for any respiratory condition