On May 23 I reported that their OPS relative to the league average was just 81.
Now their OPS is .605 while the league OPS is .731. The ratio is now .8276. Multiplying that by 100 and rounding gives them a relative OPS now of 83. That would still be the lowest ever in either the AL or NL. See the May 23 post Astros Offense On Record Setting Low Pace which shows the worst 10 teams in both AL and NL history.
But this is not park adjusted. Baseball Reference has OPS+, which is park adjusted. It is calculated a little differently. Here is the formula:
100*[OBP/lg OBP + SLG/lg SLG - 1]
The Astros now have an OPS+ of 62. See this Baseball Reference link. The lowest team OPS+ I found going all the way back to 1920 was 69 for the 1920 Philadelphia A's. The next lowest so far this year in either league is Pittsburgh with 80.