Unless commenced within thirty days after the date of the filing of the certificate of the canvass of an election on the proposition of creating a new public hospital district pursuant to chapter 70.44 RCW, no lawsuit whatever may be maintained challenging in any way the legal existence of such district or the validity of the proceedings had for the organization and creation thereof. If the creation of a district is not challenged within the period specified in this section, the district conclusively shall be deemed duly and regularly organized under the laws of this state.