Today the CDC began reporting on “probable” cases of the H1N1 influenza virus along with reporting on “confirmed” cases. This explains the large increase in cases. Specifically, this morning the CDC reported 286 laboratory “confirmed” cases in 36 states. This afternoon, CDC reported 789 “probable” cases in 44 states.
The CDC states that reporting “probable” cases will better reflect the true impact of the H1N1 flu. CDC notes too that they want to move away from focusing on numbers, since CDC knows the H1N1 flu is widespread, to focusing on the virus’ movement through the population. This is similar to how CDC monitors seasonal influenza.
Probable cases of H1N1 are reported to CDC by state health departments and occur in people who test positive for influenza A virus infection at their state health department laboratory, but those test samples have not had confirmatory testing for the novel H1N1 flu strain. To date, 99% of “probable” cases sent to CDC by state health departments have been laboratory confirmed as the novel H1N1 flu strain.
CDC has begun distributing to states the diagnostic test to detect the virus. This will allow states to test at the state level and they will no longer need to send samples to the CDC for confirmation, which will speed up the ability of states to identify new cases. Given the rapid spread of this virus, CDC anticipates that it soon will become difficult to count individuals cases.
The median age for H1N1 influenza remains 16 years, with 62% of the cases under 18 years old. The oldest patient is 81 years. The severity of the disease seems similar to seasonal flu, which is good. CDC is considering revising its school closure guidance to rely more on personal responsibility—students who have symptoms should stay home, but school will remain open.
Even though much of the news is encouraging, CDC still expects that more cases, more hospitalizations and more deaths will occur over the coming days and weeks.