Background: \- Viral infections are an important cause of illness and death in hospitalized patients as well as outpatients. New strains of viruses may appear and infect both healthy people and those with weak immune systems. A better understanding of these new virus strains (such as SARS-CoV-2, the virus that causes COVID-19) may help to control and prevent these infections. In particular, some viral infections that are less problematic in healthy persons can be life threatening in persons with weak immune systems, and viruses may be able to evolve more rapidly in persons with weak immune systems and therefore develop resistance to existing treatments. Researchers are interested in collecting samples and information from otherwise healthy persons or persons with weak immune systems to study the effects of viruses and their development.

Objectives: \- To collect samples and data from individuals who have been exposed to or have contracted viral infections.

Eligibility: * Individuals of all ages who have been diagnosed with a viral infection are suspected to have a viral infection, or have been in close contact with someone with a suspected or actual viral infection that is of interest to investigators in the Laboratory of Infectious Diseases. * Healthy persons and persons with weak immune systems (immunocompromised individuals) are eligible to participate.

Design: * Participants will be pre-screened to determine if they meet the eligibility criteria for the trial. * If eligible, evaluation may include a medical chart review, a history and physical examination, review of clinical reports from outside hospitals and laboratories, and review of tissue biopsies. * Study procedures may include collection of blood, urine, saliva, nasal fluid sampling, throat swabs, stool, and genital swabs. For participants who have specimens collected as part of their medical care (e.g. wound swabs, spinal tap, bronchoscopy, liver biopsy etc.), researchers may use leftover specimens from the clinical laboratory for testing. * Specimens may be collected up to 4 times per week during the first 2 weeks after enrollment, and then as many as 2 times per week for up to 2 years. Some participants may be asked to continue providing specimens if there is concern for relapse or recurrence of the infection. * Treatment is not offered under this study.