a pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread rapidly from Wuhan, Hubei Province, China, to all over the world. 1 As of April 20, 2020, SARS-CoV-2 has been responsible for 2 414 595 infections and 165 174 deaths worldwide, with Italy accounting for 178 972 cases and 23 660 deaths. 2 The clinical spectrum of COVID-19 ranges from an asymptomatic or mild flu-like illness to a severe pneumonia and systemic disease requiring critical care. Main symptoms are fever, dry or productive cough, and dyspnea. 3 Human strains of coronavirus have been demonstrated to invade the central nervous system through the olfactory neu-roepithelium and propagate from within the olfactory bulb. 4 Furthermore, nasal epithelial cells display the highest expression of the SARS-CoV-2 receptor, angiotensin converting enzyme 2, in the respiratory tree. 5 Smell impairment was first observed among other neurologic manifestations of COVID-19 in hospitalized patients, 6 and subsequently has been reported to be a common symptom reported in patients with mild disease. 7,8 Recently, we reported the prevalence of altered smell or taste to be 64% among a case series of 202 mildly symptomatic home-isolated patients with confirmed SARS-CoV-2 infection. 8 The aim of this study was to evaluate the evolu-IMPORTANCE An altered sense of smell and taste has been reported to be associated with coronavirus disease 2019 (COVID-19). To understand the evolution of these symptoms during the course of the disease is important to identify patients with persistent loss of smell or taste and estimate the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection on the burden of olfactory and gustative dysfunctions.OBJECTIVE To evaluate the evolution of the loss of sense of smell and taste in a case series of mildly symptomatic patients with SARS-CoV-2 infection. DESIGN, SETTING, AND PARTICIPANTSThis cross-sectional survey-based study included 202 mildly symptomatic adults (Ն18 years) consecutively assessed at Treviso Regional Hospital, Italy, between March 19 and March 22, 2020, who tested positive for SARS-CoV-2 RNA by polymerase chain reaction on nasopharyngeal and throat swabs. MAIN OUTCOMES AND MEASURESPrevalence of altered sense of smell and taste at follow-up and their variation from baseline. RESULTSOf 202 patients completing the survey at baseline, 187 (92.6%) also completed the follow-up survey (103 [55.1%] women; median age, 56 years). The evaluation of the evolution of altered sense of smell or taste in the 113 patients reporting sudden onset of these symptoms at baseline showed that 55 patients (48.7%; 95% CI, 39.2-58.3) reported complete resolution of smell or taste impairment, 46 (40.7%; 95% CI, 31.6-50.4) reported an improvement in the severity, and only 12 (10.6%; 95% CI, 5.6-17.8) reported the symptom was unchanged or worse. Persistent loss of smell or taste was not associated with persistent SARS-CoV-2 infection.CONCLUSIONS AND RELEVANCE At 4 wee...

After irradiation at 3655 A of an aqueous frozen solution containing thymine and psoralen, a new photocompound was isolated by column chromatography. It contains a furocoumarin and a pyrimidinemoiety linked together by the formation of a cyclobutane ring (see formulas I1 and IU). By irradiation at 2537 A in acetic acid solution, the photocompound breaks up again yielding psoralen and thymine. From an aqueous frozen solution containing cytosine and psoralen irradiated at 3655 A, an analogous photocompound was obtained, which, however, consists of the addition to psoralen of a uracil molecule, instead of a cytosine one (IV, V). It has been stated that the hydrolytic deamination of the cytosine moiety to the uracil one takes place during the working up of the photocompound in aqueous solution after irradiation. Substances with properties similar to those above were obtained from bergapten (5-methoxy-psoralen) and thymine, from psoralen and thymidine or thymidylic acid, irradiated at 3655 A.The new substances may be considered as model compounds in explaining the photoreactions which take place between the skin-photosensitizing furocoumarins and DNA upon irradiation at 3655 A.

A furocoumarin intercalated between two base pairs of native DNA can photoreact with two pyrimidine bases engaging both its 4',5'- and its 3,4-double bond. This fact was evidenced studying the behaviour of the fluorescence acquired by DNA during irradiation at 365 nm. When this double reaction occurs, a cross-linking is formed between the two strands of DNA, as denaturation and renaturation experiments have demonstrated. The various furocoumarin derivatives have a very diverse ability to form cross-linkages, which is independent of their photobinding capacity. This different ability is due mainly to the structure of furocoumarins and to the steric relationships that the intercalated furocoumarin molecules have with the stacked pyrimidine bases.

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