(a) Isolation of Patient. The patient shall be isolated in accordance with Section 2516 until 2 cultures from the throat and 2 from the nose, taken not less than 24 hours apart, fail to show the presence of diphtheria bacilli, except that upon clinical recovery and where antibiotics have been used as therapy, isolation may be modified in accordance with Section 2518. Release cultures may not be taken less than seven days after discontinuance of such therapy. Isolation may be terminated if the bacilli cultured from the case are proved to be virulent.

(b) Control of Household Contacts. All household contacts shall be kept under daily medical observation for clinical evidence of diphtheria for seven days after last exposure. These contacts shall be isolated if they are found to have sore throat or nasal discharge until proved by culture not to have diphtheria. All household contacts under the age of 15 shall be quarantined for at least seven days after the last exposure to the case. Nose and throat cultures for diphtheria should then be taken and the contacts may be released from quarantine if such cultures are negative. If the contact has received an antibiotic, release cultures may not be taken less than seven days after discontinuation of such medication.

(c) Release of Carriers From Isolation. Convalescent or healthy carriers of diphtheria bacilli may be released from quarantine if the bacilli are shown to be avirulent by appropriate laboratory tests. Any person who has been free from the symptoms of diphtheria for four weeks or longer and who harbors virulent diphtheria bacilli is defined as a chronic carrier. Efforts should be made to eliminate the carrier state in such persons by appropriate medical or surgical measures. If these measures are unsuccessful or are refused the health officer may release the carrier from isolation when, in his judgment, such release is not detrimental to the public health, except that the carrier may not be permitted to engage in any occupation which involves handling of foods of close association with children outside his own family.

(d) Laboratory Tests for the Release of Cases or Carriers. Cultures or virulence tests for the release of diphtheria cases or carriers shall be taken not less than seven days after discontinuation of antibiotic therapy and examined in accordance with the provisions of Section 2534.

(e) Cases on Dairies. When a case of diphtheria occurs or is confined on the premises where milk or milk products are handled, the health officer shall prohibit the use, sale or disposal of such milk or milk product, except by a method approved by him, until he is satisfied that such products are safe for human consumption.

(f) Immunization. The health officer shall take appropriate measures to encourage and facilitate a continuing program of active immunization against diphtheria for all children within his jurisdiction.