ImportanceSARS-CoV-2 infection is associated with persistent, relapsing, or new symptoms or other health effects occurring after acute infection, termed postacute sequelae of SARS-CoV-2 infection (PASC), also known as long COVID. Characterizing PASC requires analysis of prospectively and uniformly collected data from diverse uninfected and infected individuals.ObjectiveTo develop a definition of PASC using self-reported symptoms and describe PASC frequencies across cohorts, vaccination status, and number of infections.Design, Setting, and ParticipantsProspective observational cohort study of adults with and without SARS-CoV-2 infection at 85 enrolling sites (hospitals, health centers, community organizations) located in 33 states plus Washington, DC, and Puerto Rico. Participants who were enrolled in the RECOVER adult cohort before April 10, 2023, completed a symptom survey 6 months or more after acute symptom onset or test date. Selection included population-based, volunteer, and convenience sampling.ExposureSARS-CoV-2 infection.Main Outcomes and MeasuresPASC and 44 participant-reported symptoms (with severity thresholds).ResultsA total of 9764 participants (89% SARS-CoV-2 infected; 71% female; 16% Hispanic/Latino; 15% non-Hispanic Black; median age, 47 years [IQR, 35-60]) met selection criteria. Adjusted odds ratios were 1.5 or greater (infected vs uninfected participants) for 37 symptoms. Symptoms contributing to PASC score included postexertional malaise, fatigue, brain fog, dizziness, gastrointestinal symptoms, palpitations, changes in sexual desire or capacity, loss of or change in smell or taste, thirst, chronic cough, chest pain, and abnormal movements. Among 2231 participants first infected on or after December 1, 2021, and enrolled within 30 days of infection, 224 (10% [95% CI, 8.8%-11%]) were PASC positive at 6 months.Conclusions and RelevanceA definition of PASC was developed based on symptoms in a prospective cohort study. As a first step to providing a framework for other investigations, iterative refinement that further incorporates other clinical features is needed to support actionable definitions of PASC.

In the title compound, C11H15N3O2S, the dihedral angle between the mean planes of the benzene ring and hydrazinecarbo­thio­amide group is 9.2 (1)°. An intra­molecular O—H⋯N hydrogen bond is observed, serving to maintain an approximately planar conformation for the molecule. In the crystal, inversion dimers linked by C—H⋯O inter­actions occur. Further C—H⋯O contacts link dimers into (010) chains.

(7)˝, β = 92.413(6)˝, and γ = 90.654(7)˝. DFT B3LYP/6-31(G) geometry optimized molecular orbital calculations were also performed and frontier molecular orbitals of each compound are displayed. The correlations between the calculated molecular orbital energies (eV) for the surfaces of the frontier molecular orbitals to the electronic excitation transitions from the absorption spectra of each compound have been proposed. Additionally, similar correlations observed among three closely related compounds, (4), 2-[1-(2-hydroxy-4-methoxyphenyl)ethylidene]-N-methyl-hydrazinecarbothioamide, (5), 2-[1-(2-hydroxy-6-methoxyphenyl)ethylidene]-N-methyl-hydrazinecarbothioamide acetonitrile monosolvate and (6), 2-[1-(2-hydroxy-6-methoxyphenyl)ethylidene]-N-ethyl-hydrazinecarbothioamide, examining structural differences from the substitution of the methoxy group from the phenyl ring (4, 5, or 6 position) and the substitution of the terminal amine (methyl or ethyl) to their frontier molecular orbital surfaces and from their Density Functional Theory (DFT) molecular orbital energies provide further support for the suggested assignments of the title compounds.

In the title compound, C16H16N4OS, an intra­molecular C—H⋯S hydrogen bond is observed. With the exception of the phenyl ring of the phenyl­propyl­idene unit, the remainder of the mol­ecule has an almost planar skeleton with an r.m.s. deviation of 0.121 (5) Å from the plane through the remaining 16 atoms. In the crystal O—H⋯N hydrogen bonds are observed between the terminal hy­droxy­imino groups, forming inverson dimers with R 2 2(6) graph-set motifs. Additional C—H⋯N contacts stack the dimers along [100]. While no π—π inter­actions are present, weak C—H⋯O and O—H⋯Cg inter­actions are also observed and help stabilize the crystal packing.

The asymmetric unit of the title compound, C12H17N3O2S, contains two independent mol­ecules, A and B. Both mol­ecules are nearly planar with the dihedral angle between the mean planes of the thio­amide group and benzene ring being 7.5 (1)° in A and 4.3 (2)° in B. In each mol­ecule, the hy­droxy group participates in intra­molecular O—H⋯N hydrogen bonding, while the amino H atom is not involved in hydrogen bonding because of the steric hinderence caused by two neighboring methyl groups. In the crystal, the individual molecules are linked by weak C—H⋯O hydrogen bonds, forming A–A and B–B inversion dimers. The dimers are linked via C—H⋯π inter­actions which help stabilize the packing.