The H1N1 — "Swine Flu" — virus has now spread to 48 states, according to the U.S. Centers for Disease Control and Prevention (CDC). There are presently 5,710 confirmed cases.

Forty countries have officially reported 9,830 cases of influenza A(H1N1) infection, including 79 deaths, according to the World Health Organization (WHO); 5,123 cases have been confirmed in the United States.

New York City is among the hardest-hit areas in the U.S. At least 26 schools have been closed there and an assistant school principal died over the weekend of complications from the H1N1 flu.

The closings are also having an effect on schools that remain open, as worried parents keep children home. In what Department of Education officials call a "significant drop," on Tuesday only 85.5 percent of New York City's 1.1 million students were present, compared with 88.5 percent a week before. In Queens, only 83.2 percent of students were present for school on Tuesday.

We continue to see a rising tide of flu in many parts of New York City, said New York City Health Commissioner Thomas R. Frieden. As the virus spreads, we will look to slow transmission within the individual school communities by closing individual schools. Unfortunately, we fully expect to see more severe illness in the coming days, particularly among people who have underlying health problems."

New York officials said Monday's death of a 16-month-old toddler was not related to swine flu. Jonathan Zamora of Queens was admitted to Elmhurst Hospital with flu-like symptoms and later died.

Emergency rooms throughout New York filled up with concerned parents and sick children. ABC News reported more than 400 people crowded the emergency department at Elmhurst after the Zamora toddler's death.

Table. U.S. Human Cases of H1N1 Flu Infection
(As of May 20, 2009, 11:00 AM ET)
States*Confirmed and Probable CasesDeaths
Alabama
64 cases
0 deaths
Arkansas
3 cases
0 deaths
Arizona
488 cases
2 deaths
California
553 cases
0 deaths
Colorado
55 cases
0 deaths
Connecticut
59 cases
0 deaths
Delaware
88 cases
0 deaths
Florida
122 cases
0 deaths
Georgia
25 cases
0 deaths
Hawaii
26 cases
0 deaths
Idaho
8 cases
0 deaths
Illinois
794 cases
0 deaths
Indiana
105 cases
0 deaths
Iowa
71 cases
0 deaths
Kansas
34 cases
0 deaths
Kentucky**
20 cases
0 deaths
Louisiana
73 cases
0 deaths
Maine
9 cases
0 deaths
Maryland
39 cases
0 deaths
Massachusetts
175 cases
0 deaths
Michigan
171 cases
0 deaths
Minnesota
39 cases
0 deaths
Mississippi
5 cases
0 deaths
Missouri
20 cases
1 deaths
Montana
9 cases
0 deaths
Nebraska
28 cases
0 deaths
Nevada
33 cases
0 deaths
New Hampshire
22 cases
0 deaths
New Jersey
22 cases
0 deaths
New Mexico
68 cases
0 deaths
New York
284 cases
1 deaths
North Carolina
12 cases
0 deaths
North Dakota
5 cases
0 deaths
Ohio
13 cases
0 deaths
Oklahoma
43 cases
0 deaths
Oregon
94 cases
0 deaths
Pennsylvania
55 cases
0 deaths
Rhode Island
8 cases
0 deaths
South Carolina
36 cases
0 deaths
South Dakota
4 cases
0 deaths
Tennessee
86 cases
0 deaths
Texas
556 cases
3 deaths
Utah
72 cases
0 deaths
Vermont
1 cases
0 deaths
Virginia
23 cases
0 deaths
Washington
411 cases
1 death
Washington, D.C.
13 cases
0 deaths
Wisconsin
766 cases
0 deaths
TOTAL*(48)
5,710 cases
8 deaths
*includes the District of Columbia **one case is resident of KY but currently hospitalized in GA. This table will be updated daily Monday-Friday at around 11 AM ET. International Human Cases of Swine Flu Infection
See: World Health Organization. NOTE: Because of daily reporting deadlines, the state totals reported by CDC may not always be consistent with those reported by state health departments. If there is a discrepancy between these two counts, data from the state health departments should be used as the most accurate number.

No more dangerous than regular flu

Although the new flu virus continues to spread rapidly, it is still no more dangerous than regular flu, U.S. health officials say. Patients hospitalized with the flu who have underlying problems usually fare worse than otherwise healthy people who have also been hospitalized.

In an early release of the U.S. Centers for Disease Control and Prevention's journal Morbidity and Mortality Weekly Report, California health authorities assessed 30 people hospitalized for the H1N1 swine flu. One difference between these patients and patients with seasonal flu was their average age. At 27, the swine flu patients were much younger than most patients with seasonal flu who required hospitalization.

Health officials in both the United States and abroad have previously reported that the H1N1 swine flu seems to be targeting teens and young adults, unlike the regular flu, which usually strikes hardest at the elderly and the very young.

About two-thirds of the hospitalized patients in California had at least one underlying medical condition that put them at higher risk for influenza and its complications, Dr. Anne Schuchat, the CDC's interim deputy director for science and public health program, said during an afternoon teleconference Tuesday.

"The most common conditions were chronic lung disease, conditions associated with immunosuppression, chronic heart disease, obesity and pregnancy. There were five pregnant women in this series of patients," she said.

"Although the majority of hospitalized people infected with this new H1N1 virus recovered without complications, certain people did have severe and prolonged disease," Schuchat said. "None of these patients died. There are still some of these patients in the hospital, so we don't know whether they will make it or not."

Find out everything you need to know about swine flu.