** Sterilization solutions and lab testing firm Sotera Health's SHC.O shares off 1% at $15.28 in extended trading after secondary offering launched

** Broadview Heights, Ohio-based firm says private equity firms Warburg Pincus and GTCR to offload ~31.84 mln shares

** Prior to offering, Warburg owned ~19.1 mln shares for ~6.7% stake and GTCR owned ~12.74 mln shares for ~4.5% of SHC's ~285.17 mln shares outstanding, per LSEG data

** Goldman Sachs is underwriter for the offering

** Warburg and GTCR sold shares in a Mar secondary offering priced at $15.40

** SHC shares ended down 2.2% at $15.43 on Mon, down 12.5% YTD

** Avg rating of 11 analysts is "buy"; median PT $20