Conn. Gen. Stat. § 47a § 47a-15

Prior to the commencement of a summary process action, except in the case in which the landlord elects to proceed under sections 47a-23 to 47a-23b, inclusive, to evict based on nonpayment of rent, on conduct by the tenant which constitutes a serious nuisance or on a violation of subsection (h) of section 47a-11, if there is a material noncompliance with section 47a-11 which materially affects the health and safety of the other tenants or materially affects the physical condition of the premises, or if there is a material noncompliance by the tenant with the rental agreement or a material noncompliance with the rules and regulations adopted in accordance with section 47a-9, and the landlord chooses to evict based on such noncompliance, the landlord shall deliver a written notice to the tenant specifying the acts or omissions constituting the breach and that the rental agreement shall terminate upon a date not less than fifteen days after receipt of the notice. If such breach can be remedied by repair by the tenant or payment of damages by the tenant to the landlord, and such breach is not so remedied within such fifteen-day period, the rental agreement shall terminate except that (1) if the breach is remediable by repairs or the payment of damages and the tenant adequately remedies the breach within such fifteen-day period, the rental agreement shall not terminate; or (2) if substantially the same act or omission for which notice was given recurs within six months, the landlord may terminate the rental agreement in accordance with the provisions of sections 47a-23 to 47a-23b, inclusive. For the purposes of this section, “serious nuisance” means (A) inflicting bodily harm upon another tenant or the landlord or threatening to inflict such harm with the present ability to effect the harm and under circumstances which would lead a reasonable person to believe that such threat will be carried out, (B) substantial and wilful destruction of part of the dwelling unit or premises, (C) conduct which presents an immediate and serious danger to the safety of other tenants or the landlord, or (D) using the premises or allowing the premises to be used for prostitution or the illegal sale of drugs or, in the case of a housing authority, using any area within fifteen hundred feet of any housing authority property in which the tenant resides for the illegal sale of drugs. If the landlord elects to evict based upon an allegation, pursuant to subsection (g) of section 47a-11, that the tenant failed to require other persons on the premises with his consent to conduct themselves in a manner that will not constitute a serious nuisance, and the tenant claims to have had no knowledge of such conduct, then, if the landlord establishes that the premises or, in the case of a landlord that is a housing authority, the premises or any area within fifteen hundred feet of any housing authority property in which the tenant resides has been used for the illegal sale of drugs, the burden shall be on the tenant to show that he had no knowledge of the creation of the serious nuisance.