A fourth case of swine flu has been reported in San Diego. Health officials have confirmed the illness is the same strain of influenza that has killed at least 60 people and sickened close to 1,000 people in Mexico City, leading to the closure of public buildings in an attempt to stop the spread. 

Dozens of students at a private school in New York are also being tested after coming down with a flu-like illness following a trip to Mexico.  A planned event at the school was cancelled late Friday night, but authorities there have yet to confirm if it is the swine flu.

A strain of swine flu found in San Diego and Imperial counties is the same one that has killed dozens of people in Mexico, the head of the U.S. Centers for Disease and Prevention said today.

"From everything we know to date, the virus appears to be the same," Dr. Richard Besser, acting director of the CDC, said in a conference call with reporters. "So far, the genetic elements we have looked at are the same."

Four people in San Diego County have come down with swine flu, along with two in Imperial County and two in Texas.

The most recent confirmed case involved a 7-year-old boy in the San Diego area, who has recovered.

The symptoms in the local cases have been mild and are similar to regular influenza, according to the San Diego County Health and Human Services Agency.

A swine flu outbreak in Mexico has killed as many as 60 people and sickened nearly 1,000. The outbreak has forced health officials in Mexico City to close schools and keep sick residents home from work in an effort to stem the spread of the disease.

Besser said the CDC is working with the World Health Organization to respond "as rapidly as possible to this threat."

"We do not know whether this swine flu virus or some other influenza virus will lead to the next pandemic," he said. "However, scientists around the world continue to monitor the virus and take its threat seriously."

"This is something we are worried about and we are treating seriously," Besser said.

The initial steps toward the development of a vaccine have already begun, he said.

One of the San Diego residents infected with swine flu had traveled to Mexico, but it was unclear if that is where the person became infected, Besser said.

The CDC has issued an outbreak notice for Mexico, but has not called for any domestic or international travel restrictions.

Besser said the CDC has sent teams to California and Texas to help local health officials identify people who are potentially infected with swine flu.

A team will also be sent to Mexico.

Dr. Wilma Wooten, the county's public health officer, said that while the outbreak of swine flu is a "concern," it is "not a pandemic situation."

"There is always a possibility that any new virus could lead to a pandemic, but at this time the World Health Organization has not determined that we have a pandemic," she said.

Wooten said that health officials expect to identify more cases of swine flu locally due to stepped-up surveillance.

"It is anticipated that we will see additional cases of human infection with swine influenza because we have heightened our surveillance and put area health care providers on alert," Wooten said.

"We continue to work closely with the CDC, the California Department of Public Health and the Imperial County Public Health Department to investigate the source of these cases," she said.

Swine flu is a respiratory disease found in pigs that sometimes infects humans, according to the HHSA. Human cases of swine flu usually occur in people who have been in close proximity to infected pigs, but that did not appear to be the case in the latest infections, health officials said.

Symptoms of swine flu in people are similar to the symptoms of regular seasonal influenza and include fever, lethargy, coughing and a lack of appetite, according to the HHSA.

Besser said people can avoid spreading the disease by covering coughs and sneezes and washing hands frequently.

Residents should see their doctor if they have fever, cough, sore throat, body aches, headaches chills and fatigue, he said.

The Health and Human Services Department will provide updates throughout the weekend.  Check this website cbs8.com and watch News 8 at 5pm for the very newest information.