Lyn Finelli

Hospitalized Patients with 2009 H1N1 Influenza in the United States, April–June 2009

BACKGROUNDnDuring the spring of 2009, a pandemic influenza A (H1N1) virus emerged and spread globally. We describe the clinical characteristics of patients who were hospitalized with 2009 H1N1 influenza in the United States from April 2009 to mid-June 2009.nnnMETHODSnUsing medical charts, we collected data on 272 patients who were hospitalized for at least 24 hours for influenza-like illness and who tested positive for the 2009 H1N1 virus with the use of a real-time reverse-transcriptase-polymerase-chain-reaction assay.nnnRESULTSnOf the 272 patients we studied, 25% were admitted to an intensive care unit and 7% died. Forty-five percent of the patients were children under the age of 18 years, and 5% were 65 years of age or older. Seventy-three percent of the patients had at least one underlying medical condition; these conditions included asthma; diabetes; heart, lung, and neurologic diseases; and pregnancy. Of the 249 patients who underwent chest radiography on admission, 100 (40%) had findings consistent with pneumonia. Of the 268 patients for whom data were available regarding the use of antiviral drugs, such therapy was initiated in 200 patients (75%) at a median of 3 days after the onset of illness. Data suggest that the use of antiviral drugs was beneficial in hospitalized patients, especially when such therapy was initiated early.nnnCONCLUSIONSnDuring the evaluation period, 2009 H1N1 influenza caused severe illness requiring hospitalization, including pneumonia and death. Nearly three quarters of the patients had one or more underlying medical conditions. Few severe illnesses were reported among persons 65 years of age or older. Patients seemed to benefit from antiviral therapy.

H1N1 2009 influenza virus infection during pregnancy in the USA

BACKGROUNDnPandemic H1N1 2009 influenza virus has been identified as the cause of a widespread outbreak of febrile respiratory infection in the USA and worldwide. We summarised cases of infection with pandemic H1N1 virus in pregnant women identified in the USA during the first month of the present outbreak, and deaths associated with this virus during the first 2 months of the outbreak.nnnMETHODSnAfter initial reports of infection in pregnant women, the US Centers for Disease Control and Prevention (CDC) began systematically collecting additional information about cases and deaths in pregnant women in the USA with pandemic H1N1 virus infection as part of enhanced surveillance. A confirmed case was defined as an acute respiratory illness with laboratory-confirmed pandemic H1N1 virus infection by real-time reverse-transcriptase PCR or viral culture; a probable case was defined as a person with an acute febrile respiratory illness who was positive for influenza A, but negative for H1 and H3. We used population estimates derived from the 2007 census data to calculate rates of admission to hospital and illness.nnnFINDINGSnFrom April 15 to May 18, 2009, 34 confirmed or probable cases of pandemic H1N1 in pregnant women were reported to CDC from 13 states. 11 (32%) women were admitted to hospital. The estimated rate of admission for pandemic H1N1 influenza virus infection in pregnant women during the first month of the outbreak was higher than it was in the general population (0.32 per 100 000 pregnant women, 95% CI 0.13-0.52 vs 0.076 per 100 000 population at risk, 95% CI 0.07-0.09). Between April 15 and June 16, 2009, six deaths in pregnant women were reported to the CDC; all were in women who had developed pneumonia and subsequent acute respiratory distress syndrome requiring mechanical ventilation.nnnINTERPRETATIONnPregnant women might be at increased risk for complications from pandemic H1N1 virus infection. These data lend support to the present recommendation to promptly treat pregnant women with H1N1 influenza virus infection with anti-influenza drugs.nnnFUNDINGnUS CDC.

Estimates of the Prevalence of Pandemic (H1N1) 2009, United States, April–July 2009

Through July 2009, a total of 43,677 laboratory-confirmed cases of influenza A pandemic (H1N1) 2009 were reported in the United States, which is likely a substantial underestimate of the true number. Correcting for under-ascertainment using a multiplier model, we estimate that 1.8 million–5.7 million cases occurred, including 9,000–21,000 hospitalizations.

Public health impact of including two lineages of influenza B in a quadrivalent seasonal influenza vaccine

The annual trivalent influenza vaccine (TIV) includes viruses representing three influenza strains - one A/H1N1, one A/H3N2, and one B, although two antigenically distinct lineages of influenza B (Victoria and Yamagata) co-circulate annually in the United States. Predicting which lineage of influenza B will predominate during a season is challenging, and cross-protection by immunization against the other lineage is expected to be low. One proposed alternative is to produce a quadrivalent influenza vaccine (QIV) including an influenza B virus from each of the two circulating lineages. We estimated the additional public health benefit of QIV compared with TIV by calculating the expected impact on influenza-related health outcomes (illness, hospitalization, and death) over ten influenza seasons (1999/2000-2008/2009). We included data on the annual incidence of influenza-associated outcomes, virologic circulation, vaccine coverage, and vaccine effectiveness. We also considered annual vaccine production capacity, since available resources would have produced four vaccine viruses instead of three, potentially resulting in fewer doses of QIV. Use of QIV could have reduced annual cases (range: 2200-970,000), hospitalizations (range: 14-8200), and deaths (range: 1-485) in the US. During earlier seasons, adjusting production capacity for a fourth virus in QIV could have resulted in reduced overall influenza vaccine availability and net increases in influenza-associated outcomes. However, in recent seasons, the expected supply of QIV is likely to exceed the doses of vaccine actually administered. The potential net impact of QIV on influenza-associated outcomes is expected to vary between seasons, depending on annual variability in the incidence of influenza caused by the two influenza B lineages, vaccine coverage, and effectiveness. The additional protection provided by including a second lineage of influenza B could result in a modest reduction in influenza-associated outcomes.

Impact of maternal immunization on influenza hospitalizations in infants

We sought to determine whether maternal vaccination during pregnancy was associated with a reduced risk of laboratory-confirmed influenza hospitalizations in infants <6 months old. Active population-based, laboratory-confirmed influenza surveillance was conducted in children hospitalized with fever and/or respiratory symptoms in 3 US counties from November through April during the 2002 through 2009 influenza seasons. The exposure, influenza vaccination during pregnancy, and the outcome, positive/negative influenza testing among their hospitalized infants, were compared using logistic regression analyses. Among 1510 hospitalized infants <6 months old, 151 (10%) had laboratory-confirmed influenza and 294 (19%) mothers reported receiving influenza vaccine during pregnancy. Eighteen (12%) mothers of influenza-positive infants and 276 (20%) mothers of influenza-negative infants were vaccinated (unadjusted odds ratio, 0.53; 95% confidence interval, 0.32-0.88 and adjusted odds ratio, 0.52; 95% confidence interval, 0.30-0.91). Infants of vaccinated mothers were 45-48% less likely to have influenza hospitalizations than infants of unvaccinated mothers. Our results support the current influenza vaccination recommendation for pregnant women.

Staphylococcus aureus Community-Acquired Pneumonia During the 2006 to 2007 Influenza Season

STUDY OBJECTIVEnStaphylococcus aureus is a cause of community-acquired pneumonia that can follow influenza infection. In response to a number of cases reported to public health authorities in early 2007, additional case reports were solicited nationwide to better define S. aureus community-acquired pneumonia during the 2006 to 2007 influenza season.nnnMETHODSnCases were defined as primary community-acquired pneumonia caused by S. aureus occurring between November 1, 2006, and April 30, 2007. Case finding was conducted through an Emerging Infections Network survey and through contacts with state and local health departments.nnnRESULTSnOverall, 51 cases were reported from 19 states; 37 (79%) of 47 with known susceptibilities involved infection with methicillin-resistant S. aureus (MRSA). The median age of case patients was 16 years, and 44% had no known pertinent medical history. Twenty-two (47%) of 47 case patients with information about other illnesses were diagnosed with a concurrent or antecedent viral infection during their illness, and 11 of 33 (33%) who were tested had laboratory-confirmed influenza. Of the 37 patients with MRSA infection, 16 (43%) were empirically treated with antimicrobial agents recommended for MRSA community-acquired pneumonia. Twenty-four (51%) of 47 patients for whom final disposition was known died a median of 4 days after symptom onset.nnnCONCLUSIONnS. aureus continues to cause community-acquired pneumonia, with most reported cases caused by MRSA and many occurring with or after influenza. In this series, patients were often otherwise healthy young people and mortality rates were high. Further prospective investigation is warranted to clarify infection incidence, risk factors, and preventive measures.

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

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.

Epidemiology of 2009 Pandemic Influenza A (H1N1) Deaths in the United States, April–July 2009

During the spring of 2009, pandemic influenza A (H1N1) virus (pH1N1) was recognized and rapidly spread worldwide. To describe the geographic distribution and patient characteristics of pH1N1-associated deaths in the United States, the Centers for Disease Control and Prevention requested information from health departments on all laboratory-confirmed pH1N1 deaths reported from 17 April through 23 July 2009. Data were collected using medical charts, medical examiner reports, and death certificates. A total of 377 pH1N1-associated deaths were identified, for a mortality rate of .12 deaths per 100,000 population. Activity was geographically localized, with the highest mortality rates in Hawaii, New York, and Utah. Seventy-six percent of deaths occurred in persons aged 18-65 years, and 9% occurred in persons aged ≥ 65 years. Underlying medical conditions were reported for 78% of deaths: chronic lung disease among adults (39%) and neurologic disease among children (54%). Overall mortality associated with pH1N1 was low; however, the majority of deaths occurred in persons aged <65 years with underlying medical conditions.

Human Infections With Influenza A(H3N2) Variant Virus in the United States, 2011–2012

BACKGROUND.u2003During August 2011-April 2012, 13 human infections with influenza A(H3N2) variant (H3N2v) virus were identified in the United States; 8 occurred in the prior 2 years. This virus differs from previous variant influenza viruses in that it contains the matrix (M) gene from the Influenza A(H1N1)pdm09 pandemic influenza virus. METHODS.u2003A case was defined as a person with laboratory-confirmed H3N2v virus infection. Cases and contacts were interviewed to determine exposure to swine and other animals and to assess potential person-to-person transmission. RESULTS.u2003Median age of cases was 4 years, and 12 of 13 (92%) were children. Pig exposure was identified in 7 (54%) cases. Six of 7 cases with swine exposure (86%) touched pigs, and 1 (14%) was close to pigs without known direct contact. Six cases had no swine exposure, including 2 clusters of suspected person-to-person transmission. All cases had fever; 12 (92%) had respiratory symptoms, and 3 (23%) were hospitalized for influenza. All 13 cases recovered. CONCLUSIONS.u2003H3N2v virus infections were identified at a high rate from August 2011 to April 2012, and cases without swine exposure were identified in influenza-like illness outbreaks, indicating that limited person-to-person transmission likely occurred. Variant influenza viruses rarely result in sustained person-to-person transmission; however, the potential for this H3N2v virus to transmit efficiently is of concern. With minimal preexisting immunity in children and the limited cross-protective effect from seasonal influenza vaccine, the majority of children are susceptible to infection with this novel influenza virus.

High costs of influenza: direct medical costs of influenza disease in young children.

This study determined direct medical costs for influenza-associated hospitalizations and emergency department (ED) visits. For 3 influenza seasons, children <5 years of age with laboratory-confirmed influenza were identified through population-based surveillance. The mean direct cost per hospitalized child was