Points to consider:
1) This poll was commissioned by Peru21, a very anti-Humala publication.
2) Datum has shown results that consistently favour Keiko more than the average of polls in Peru.
3) With that said, the pollster will stand by its numbers and it does seem that Keiko is at least consolidating her small lead in the polls.
The result has a margin of error of +/-2.8% and is a national urban/rural type. 1211 people interviewed. Details here.