MEXICO CITY — Citing an ebb in the number of swine flu cases, Mexican officials said Monday that they would lower the public alert against the virus and allow most of the nation’s businesses to reopen this week, even as the outbreak, which appears to have started in Mexico, continued its spread worldwide.
In Mexico City, where most of the nation’s 26 deaths from the virus and more than 700 infections have been recorded, restaurants and other eateries will reopen on Wednesday. Churches and museums will reopen Thursday, but bars, nightclubs, cinemas and theaters will remain closed until further notice, The Associated Press reported.
Across the country, most factories and offices will reopen on Wednesday, Health Minister José Ángel Córdova said in a news conference. A decision has not yet been made to reopen schools, which have remained shuttered for well over a week.
In another sign that the disease may not be as serious as feared, Mr. Cordova said that the flu, influenza A(H1N1), appears only slightly more contagious than the seasonal flu, less than thought. Each sufferer is, on average, passing the disease along to between 1.4 and 1.8 people, a statistic known as the R factor. The number of new cases is declining in Mexico, he said, and no deaths have been reported since April 29.
Swine flu is now widespread in the United States, health officials said, and continues to spread globally. As of Monday afternoon, there were 286 confirmed cases of the disease in 36 states — up from 226 in 30 states on Sunday — and more than 700 additional cases considered probable in 44 states, Dr. Richard Besser, acting director of the Centers for Disease Control and Prevention, said at a news conference. Dr. Besser stressed that most of the cases were mild, and added that, of the 286 confirmed cases, only 35 had resulted in hospitalization.
“While we’re not out of the woods, we are seeing some encouraging signs,” he said.
The World Health Organization also said on Monday that it had counted 1,025 laboratory confirmed cases in 20 countries. On Sunday, there were 898 confirmed cases in 18 countries.
The lack of sustained transmission outside of North America has kept the World Health Organization from declaring a full-scale pandemic, but officials have warned nations not to let down their guard.
“We’re not quite certain about how this is going to evolve. There is always uncertainty when it comes to a new disease,” Dr. Keiji Fukuda, the W.H.O.’s deputy director general, said in a Monday conference call. In particular, the organization is concerned about the disease’s possible spread to the southern hemisphere, which is moving into the winter, the season most conducive to the flu’s spread.
“In this situation, its critical that we continue to maintain our alertness and surveillance,” he said.
Colombia and El Salvador were the latest countries to join the W.H.O. list, which is topped by Mexico, with roughly 60 percent of the world’s total confirmed cases, and the United States, with 23 percent of the total.
In the United States, the only known death from the disease was that of a toddler from Mexico City who died in Texas on April 27. No deaths have been reported in nations outside of Mexico and America, and throughout the world, most cases have been mild.
Spain remains the most affected country in Europe, with the health ministry saying Monday that the number of flu cases there had risen to 54. Most cases have been linked to travelers who visited Mexico, and there was no evidence of sustained human-to-human transmission of the flu anywhere in Europe, the European Center for Disease Prevention and Control reported.
Such is the concern about the disease’s spread, however, that some countries have taken extreme steps to contain it. In China, authorities have quarantined some 70 Mexican travelers in hospitals and hotels — many of whom have shown no sign of illness. A group of 25 Canadian exchange students have also been confined in the northern city of Changchun, according to Canadian university officials.
Canada has 103 confirmed cases of swine flu. The group does not have any flu symptoms, University of Montreal spokeswoman Sophie Langlois said Monday, The Associated Press reported.
In Britain, seven of the new cases reported Monday appeared “to have been acquired from person-to-person contact,” health officials said, bringing the total across the country to 27 and raising fears that the disease could begin a more sustained spread throughout the country.
Five of the new confirmed cases were children who all attended the same southeast London school, which would now be closed for seven days, Reuters reported.
For disease investigators at the W.H.O., there are still more questions than answers about the new flu strain, Dr. Fukuda said. The organization has determined that the cases of the virus have ranged from very mild to fatal, and that the disease is resulting in diarrhea in 40 to 50 percent of cases, more than in regular flu. The incubation period also may be longer than for regular flu, up to 6-8 days, Dr. Fukuda said.
In the United States, federal health officials said Sunday that more expected to turn up in additional states in the next few days.
“I think it’s circulating all over the U.S.,” Dr. Anne Schuchat, the interim deputy director for science and public health at the Centers for Disease Control and Prevention, said in a news conference. “The virus has arrived, I would say, in most of the country now.”
The good news, Dr. Schuchat said, is that most cases in the United States have been mild, and health officials in Mexico said that cases there seemed to be leveling off.
But Dr. Schuchat said, “I don’t think we’re out of the woods yet.”
She said the virus had a number of unusual features that were cause for concern. It has flared up at a time of year when the flu season is normally ending. It is new, so people probably have little or no resistance to it.
And unlike the common types of seasonal flu, it appears to infect an unusually high percentage of young people. The median age of patients is 17.
Dr. Schuchat said scientists at the C.D.C. were preparing a “seed stock” from virus samples that could be used for a vaccine.
The possibility that H1N1 might be passed back and forth between humans and pigs was discussed at a World Health Organization news teleconference from Geneva on Sunday. Canadian officials reported on Saturday that an infected farm worker had spread the virus to pigs in Alberta.
In New York, St. Francis Preparatory School, the epicenter of the swine flu outbreak in New York City, reopened for classes on Monday after being closed for a week. Fifty-nine cases, all mild, have been linked to the school. A total of 73 confirmed cases have been reported statewide.
Mayor Michael Bloomberg and city health officials — along with dozens of reporters from news organizations around the world — were there to welcome back the students to the school on Francis Lewis Boulevard in Fresh Meadows, in northeastern Queens.
The outbreak had initially sparked fears of the disease spreading quickly throughout the city and causing serious health problems, but the officials said Sunday that so far all the confirmed cases in New York have been mild; monitoring of intensive-care units throughout the city had turned up no severe cases.