Hospitalized Patients with 2009 Pandemic Influenza A (H1N1) Virus Infection in the United States—September–October 2009

Abstract

Given the potential worsening clinical severity of 2009 pandemic influenza A (H1N1) virus (pH1N1) infection from spring to fall 2009, we conducted a clinical case series among patients hospitalized with pH1N1 infection from September through October 2009. A case patient was defined as a hospitalized person who had test results positive for pH1N1 virus by real-time reverse-transcription polymerase chain reaction. Among 255 hospitalized patients, 34% were admitted to an intensive care unit and 8% died. Thirty-four percent of patients were children <18 years of age, 8% were adults ≥ 65 years of age, and 67% had an underlying medical condition. Chest radiographs obtained at hospital admission that had findings that were consistent with pneumonia were noted in 103 (46%) of 255 patients. Among 255 hospitalized patients, 208 (82%) received neuraminidase inhibitors, but only 47% had treatment started ≤ 2 days after illness onset. Overall, characteristics of hospitalized patients with pH1N1 infection in fall 2009 were similar to characteristics of patients hospitalized with pH1N1 infection in spring 2009, which suggests that clinical severity did not change substantially over this period.

Description of Hospitalized Cases of Influenza A(H1N1)pdm09 Infection on the Basis of the National Hospitalized-Case Surveillance, 2009&ndash;2010, Japan

“…CFR in those aged 20 years and older was significantly higher than that in those aged under 20 years. These results were consistent with the results from previous reports and reaffirmed that A(H1N1)pdm09 virus infection led to high morbidity in the young population and a high CFR in the elderly population (4,(7)(8)(9)(10)(11).…”

“…This rate is similar to those found in Mexico, Chile, and Brazil and 50z of the rate observed in Australia, the Unites States, and Argentina during the same period (6,7). Consistent with the results described in other reports, over 80z of hospitalized cases in the present study were young (＜20 years) (4,(7)(8)(9)(10)(11)35). It is interesting to note that the results from several studies have indicated that the elderly were not disproportionately affected by the virus, perhaps because of cross immunity to A(H1N1)pdm09 in this population (12)(13)(14).…”

“…Information pertaining to the date of ILI onset, complications, and the administration of antivirals, including whether antivirals were eventually administered when complications were diagnosed, may have better enabled us to compare and analyze associations between antiviral treatment and severe complications, including death. With regard to fatal cases, the overall CFR of hospitalized cases was 1.5z, which was remarkably low compared with CFR of 7z-11z reported from the US (3,8). As previously mentioned, however, approximately 40z of hospitalized cases had been admitted for non-therapeutic purposes.…”

“…Antivirals were administered at similar proportions among non-fatal and fatal cases (86z and 83z, respectively). The results from studies conducted in Australia, China, and the US indicated similar proportions of antiviral administration among hospitalized patients (2,22,23,36,45). Several studies have suggested that early treatment with neuraminidase inhibitors is beneficial for ILI patients and may reduce serious complications; however, the benefit of neuraminidase inhibitors remains controversial (2,22-35, 41,44,46).…”

Atopic conditions other than asthma and risk of the 2009 novel H1N1 infection in children: A case‐control study

“…A few reports from different countries identified asthma as the single most common chronic condition among hospitalized or deceased individuals with H1N1. [2][3][4][5] The literature suggests that individuals with asthma and other atopic conditions have suboptimal innate and adaptive immune functions against microbial agents.…”