The total number of confirmed US swine flu cases continues to rise: it’s currently at 64, with 45 of those cases in New York City. This is something that CDC Acting Director Richard Besser told us to expect. Because samples from flu patients have to be sent to a lab for analysis, there’s a lag between when someone with flulike symptoms shows up at a hospital or doctor’s office and when we know whether that person has this particular strain of influenza A/H1N1.

Besser and Homeland Security Secretary Janet Napolitano are also stressing that the news will get worse, but that still won’t mean that it’s time to panic. We will probably see more complicated cases (five patients are currently hospitalized) and some deaths – but, Napolitano reminds us, a normal flu season would bring 35,000 deaths, too.

Here’s CNN on the latest worldwide totals:

By early Tuesday, the swine flu outbreak in Mexico was suspected of causing 152 deaths and more than 1,600 illnesses, Mexico’s health minister told reporters.

The World Health Organization said at least 104 cases have been confirmed worldwide, including 64 in the United States; 26 in Mexico — of whom seven have died; six in Canada; three in New Zealand; two each in Spain and the United Kingdom; and one in Israel.

By Tuesday evening, WHO had not included 13 additional deaths reported in Mexico, eight additional cases reported in New Zealand and one additional case in Israel. The additional cases were confirmed by health officials in those countries.

Yesterday, the WHO raised the level of influenza pandemic alert from phase 3 to phase 4, indicating “that the likelihood of a pandemic has increased, but not that a pandemic is inevitable.