Para White Hill, de Joe Haldemann . Eu li no The Hard SF Renaissance, editado por David G. Hartwell e Kathryn Cramer. Esta antologia foi publicada em 2002, mas a história data de 1995 e você presumivelmente a leu em uma das antologias anteriores.
Após uma guerra, a Terra foi semeada com nanófagos. Eles matam as pessoas da maneira que você lembrava:
There were fewer than ten thousand people living on the blighted planet then, an odd mix of politicians, religious extremists, and academics, mostly. Almost all of them under glass. Tourists flowed through the domed-over ruins, but not many stayed long. The planet was still very dangerous over all of its unprotected surface, since the Fwndyri had thoroughly seeded it with nanophages. Those were submicroscopic constructs that sought out concentrations of human DNA. Once under the skin, they would reproduce at a geometric rate, deconstructing the body, cell by cell, building new nanophages. A person might complain of a headache and lie down, and a few hours later there would be nothing but a dry skeleton, lying in dust. When the humans were all dead, they mutated and went after DNA in general, and sterilized the world.
O protagonista está imune porque:
White Hill and I were "bred" for immunity to the nanophages. Our DNA winds backwards, as was the case with many people born or created after that stage of the war. So we could actually go through the elaborate airlocks and step out onto the blasted surface unprotected.