United States manufacturing improved again in July with a key gauge of activity rising further into expansion territory. The Institute for Supply Management, an association of purchasing managers, said Monday that its manufacturing index rose to 54.2 last month, up from a June reading of 52.6. Any reading above 50 signals that U.S. manufacturing is expanding. While it was the second straight month that the index has been above the 50 threshold, indicating manufacturing is expanding again, economists cautioned that the outlook is clouded by spreading infections in the U.S. in the South, West and Midwest. “Manufacturing is recovering from low levels and the outlook is uncertain, given the threat of repeated disruptions from virus outbreaks,” said Rubeela Farooqi, chief U.S. economist at High Frequency Economics.