During the last 5 weeks, the Mono County Health Department has received reports of 9 laboratory confirmed cases of whooping cough (pertussis). All are residents of Mammoth Lakes, and most are infants and children under 2 years of age. All except one have been fully vaccinated appropriately for their age. None have been hospitalized. At this point in time, 4 day care sites, and one school is involved, and all staff and parents have been or are being notified.