to gross receipts within the meaning of section 6033 of the Internal Revenue Code of 1986. (3) Qualified virus transmission prevention expenses The term qualified virus transmission prevention expenses means the payment or accrual of any expense which is intended to reduce or prevent the transmission of communicable viruses (including Severe Acute Respiratory Syndrome Coronavirus 2 (SARS–CoV–2)), which is used in the operation of a trade or business in the United States (including the possessions of the United States), including— (A) barriers erected to prevent virus spread between customers and employees, including plexiglass installed at cashiers and other counters, and partitions to separate customers, (B) changes to fixtures to facilitate social distancing, including additional check-out stations, (C) contactless point-of-sale systems, (D) enhanced sanitation, including deep cleaning and hand sanitizer, (E) thermometers and other virus monitoring devices or methods, including COVID–19 testing, (F) ventilation or air filtration, (G) signage related to public health awareness, social distancing, or altered services like curbside pickups, (H) employee health education, (I) training for new business procedures resulting from COVID–19, (J) personal protective equipment, and (K) such additional expenses as the Secretary, in consultation with the Secretary of Health and Human Services, determines to be necessary. (4) Secretary The term Secretary means the Secretary of the Treasury or the Secretary’s delegate. (d) Aggregation rule All persons treated as a single employer under subsection (a) or (b) of section 52 of the Internal Revenue Code of 1986, or subsection (m) or (o) of section 414 of such Code, shall be treated as one employer for purposes of this section. (e) Denial of double benefit For purposes of chapter 1 of such Code, the gross income of any eligible employer, for the taxable year which includes the last day of any calendar quarter with respect to which a credit is allowed under this section, shall be