infectious disease product means any drug or biological product for human use that— (A) is intended to treat a serious or life-threatening infection, including those caused by— (i) an antibacterial or antifungal resistant pathogen (including novel or emerging infectious pathogens), or (ii) qualifying pathogens listed by the Secretary of Health and Human Services under section 505E(f) of the Federal Food, Drug, and Cosmetic Act ( 21 U.S.C. 351 et seq.), and (B) is intended to treat an infection for which there is an unmet medical need as defined by the Secretary of Health and Human Services. (2) Special limitation on foreign testing (A) In general No credit shall be allowed under this section with respect to any clinical testing conducted outside the United States unless— (i) such testing is conducted outside the United States because there is an insufficient testing population in the United States, and (ii) such testing is conducted by a United States person or by any other person who is not related to the taxpayer to whom exemption under section 505(i) of the Federal Food, Drug, and Cosmetic Act is granted. (B) Insufficient testing population For purposes of this section, the testing population in the United States is insufficient if there are not within the United States the number of available and appropriate human subjects needed to produce reliable and timely data from the clinical investigation. (3) Certain rules made applicable Rules similar to the rules of paragraphs (1) and (2) of section 41(f) shall apply for purposes of this section. (4) Election This section shall apply to any taxpayer for any taxable year only if such taxpayer elects (at such time and in such manner as the Secretary may by regulations prescribe) to have this section apply for such taxable year. (e) Transferability (1) In general Any taxpayer holding a credit under this section may transfer for valuable consideration unused but otherwise allowable credit for use by a qualified pharmaceutical research taxpayer. A taxpayer that