The Las Vegas-area cases involved a 39-year-old woman hospitalized in critical condition but improving, and an 11-year-old boy who has recovered but has not yet returned to school, said Dr. Lawrence Sands, chief of the Southern Nevada Health District.
"While the identification of cases in Clark County is not surprising and is not cause for alarm, it underscores the importance of the public taking the necessary steps to protect their health and prevent the spread of disease," Sands said.
"I definitely expect we'll see more cases," Sands said during a news conference.
Washoe County Health District spokeswoman Judy Davis identified the two new swine flu patients in northern Nevada as the mother and a younger sibling of the state's first confirmed swine flu patient, a 2-year-old Reno girl who is recovering.
Davis said she didn't immediately know the ages of the new patients or the gender of the sibling, but said they had been in close contact with the child and were recovering. Davis said she did not know if either had been hospitalized.
Tests by the Centers for Disease Control and Prevention in Atlanta showed the swine flu virus, also identified as H1N1, in the Nevada patients, the health officials said.
Seven more samples from Nevada were being tested by the CDC, five from the Las Vegas area and one each from Reno and Carson City, said Martha Framsted, spokeswoman for the Nevada state Health Division.
The CDC was reporting at least 487 cases of the virus nationwide, including one death — a toddler from Mexico who died in Texas.
In Las Vegas, Sands compared the swine flu to common seasonal flu, and said health investigators found no connection between the two patients. He said neither traveled recently and neither had any known contact with anyone from Mexico or with an ill person.
"What this is telling us is that this is circulating in the community, just like seasonal influenza," Sands said. The virus is believed to spread person-to-person through coughing, sneezing or touching something contaminated with the flu virus.
"There is no evidence at this time it is causing more illness or more severe illness than the seasonal flu strain," he added.
Sands and Dr. John Middaugh, Clark County health director, said the seriously ill woman had improved since being hospitalized April 24 with respiratory distress.
Clark County school officials said they noticed no spike in pupil illnesses and absences at the 11-year-old boy's middle school, and decided not to close the campus.
County school Superintendent Walt Rulffes and Diana Taylor, chief nurse for the nation's fifth-largest school district, refused to name the school — one of 48 middle schools in the sprawling district of more than 300,000 students.
Sands said it was important for people to wash hands frequently, and recommended they stay home if they have flu symptoms, including fever, cough, sore throat, body aches, chills and fatigue.
"I definitely expect we'll see more cases, we'll identify more cases. ... undetected cases, more severe cases," he said. "Unfortunately, as with the influenza season we may see some deaths as well."
The Las Vegas area has about 2 million of the state's 2.7 million residents. Health district officials say the region averages about 230 deaths a year due to seasonal influenza and related pneumonia.
In Washoe County, Davis said the two siblings attended different day care centers.
Health officials have been in contact with the younger child's day care center operator and have been investigating to determine if anyone else may have become ill, she said.
The county health district did not identify the day care center.
Associated Press correspondent Scott Sonner in Reno contributed to this report.