Fatimah S. Dawood

Burden of seasonal influenza hospitalization in children, United States, 2003 to 2008.

OBJECTIVES To estimate the rates of hospitalization with seasonal influenza in children aged <18 years from a large, diverse surveillance area during 2003 to 2008. STUDY DESIGN Through the Emerging Infections Program Network, population-based surveillance for laboratory-confirmed influenza was conducted in 10 states, including 5.3 million children. Hospitalized children were identified retrospectively; clinicians made influenza testing decisions. Data collected from the hospital record included demographics, medical history, and clinical course. Incidence rates were calculated with census data. RESULTS The highest hospitalization rates occurred in children aged <6 months (seasonal range, 9-30/10 000 children), and the lowest rates occurred in children aged 5 to 17 years (0.3-0.8/10 000). Overall, 4015 children were hospitalized, 58% of whom were identified with rapid diagnostic tests alone. Forty percent of the children who were hospitalized had underlying medical conditions; asthma (18%), prematurity (15% of children aged <2 years), and developmental delay (7%) were the most common. Severe outcomes included intensive care unit admission (12%), respiratory failure (5%), bacterial coinfection (2%), and death (0.5%). CONCLUSIONS Influenza-associated hospitalization rates varied by season and age and likely underestimate true rates because many hospitalized children are not tested for influenza. The proportion of children with severe outcomes was substantial across seasons. Quantifying incidence of influenza hospitalization and severe outcomes is critical to defining disease burden.

Household Transmission of Pandemic (H1N1) 2009, San Antonio, Texas, USA, April–May 2009

Transmission rates were lower than those for seasonal influenza.

Complications and Associated Bacterial Coinfections Among Children Hospitalized With Seasonal or Pandemic Influenza, United States, 2003–2010

BACKGROUND Data on the range and severity of influenza-associated complications among children are limited. We describe the frequency and severity of complications in hospitalized children aged <18 years with seasonal influenza (during 2003-2009) and 2009 pandemic influenza A(H1N1) (during 2009-2010). METHODS Population-based surveillance for laboratory-confirmed influenza hospitalizations was conducted among 5.3 million children in 10 states. Complications were identified by International Classification of Diseases, Ninth Revision (ICD-9) codes in medical records. RESULTS During 2003-2010, 7293 children hospitalized with influenza were identified, of whom 6769 (93%) had complete ICD-9 code data. Among the 6769 children, the median length of hospitalization was 3 days (interquartile range, 2-4 days), 975 (14%) required intensive care, 359 (5%) had respiratory failure, and 40 (1%) died. The most common complications were pneumonia (in 28% of children), asthma exacerbations (in 22% [793/3616] aged ≥ 2 years), and dehydration (in 21%). Lung abscess/empyema, tracheitis, encephalopathy, bacteremia/sepsis, acute renal failure, and myocarditis were rare (each ≤ 2% of children) but associated with a median hospitalization duration of ≥ 6 days, and 48%-70% of children required intensive care. Bacterial cultures with positive results were identified in 2% of children (107/6769); Staphylococcus aureus and Streptococcus pneumoniae were most commonly identified. CONCLUSIONS Complications contribute substantially to the disease burden among children hospitalized with influenza, through intensive care requirements and prolonged hospitalization, highlighting the importance of primary prevention with influenza vaccination.

Influenza-Associated Pneumonia in Children Hospitalized With Laboratory-Confirmed Influenza, 2003-2008

Background: Pneumonia is one of the most common complications in children hospitalized with influenza. We describe hospitalized children with influenza-associated pneumonia and associated risk indicators. Methods: Through Emerging Infections Program Network population-based surveillance, children aged <18 years hospitalized with laboratory-confirmed influenza with a chest radiograph during hospitalization were identified during the 2003–2008 influenza seasons. A case with radiologically confirmed influenza-associated pneumonia was defined as a child from the surveillance area hospitalized with: (1) laboratory-confirmed influenza and (2) evidence of new pneumonia on chest radiograph during hospitalization. Hospitalized children with pneumonia were compared with those without pneumonia by univariate and multivariate analysis. Results: Overall, 2992 hospitalized children with influenza with a chest radiograph were identified; 1072 (36%) had influenza-associated pneumonia. When compared with children hospitalized with influenza without pneumonia, hospitalized children with influenza-associated pneumonia were more likely to require intensive care unit admission (21% vs. 11%, P < 0.01), develop respiratory failure (11% versus 3%, P < 0.01), and die (0.9% vs. 0.3% P = 0.01). In multivariate analysis, age 6 to 23 months (adjusted OR: 2.1, CI: 1.6–2.8), age 2 to 4 years (adjusted OR: 1.7, CI: 1.3–2.2), and asthma (adjusted OR: 1.4, CI: 1.1–1.8) were significantly associated with influenza-associated pneumonia. Conclusions: Hospitalized children with influenza-associated pneumonia were more likely to have a severe clinical course than other hospitalized children with influenza, and children aged 6 months to 4 years and those with asthma were more likely to have influenza-associated pneumonia. Identifying children at greater risk for influenza-associated pneumonia will inform prevention and treatment strategies targeting children at risk for influenza complications.

Children With Asthma Hospitalized With Seasonal or Pandemic Influenza, 2003–2009

OBJECTIVE: To describe the characteristics and clinical courses of asthmatic children hospitalized with seasonal or 2009 pandemic H1N1 influenza and compare complications by influenza type. METHODS: During the 2003–2009 influenza seasons and the 2009 pandemic, we conducted surveillance of 5.3 million children aged 17 years or younger for hospitalization with laboratory-confirmed influenza and identified those with asthma (defined as those aged 2–17 years with a history of asthma in their medical record or a discharge code for acute asthma exacerbation or status asthmaticus). We collected data from medical records on medical history and clinical course; data on asthma severity and control were not routinely collected. RESULTS: During the 2003–2009 influenza seasons, 701 (32%) of 2165 children hospitalized with influenza had asthma; during the 2009 pandemic, 733 (44%) of 1660 children had asthma. The median age of the asthmatic children was 7 years, and 73% had no additional medical conditions. Compared with asthmatic children with seasonal influenza, a higher proportion with 2009 pandemic H1N1 influenza required intensive care (16% vs 22%; P = .01) and were diagnosed with pneumonia (40% vs 46%; P = .04), whereas equal proportions had respiratory failure (5% vs 5%; P = .8) and died (1% vs 1%; P = .4). More asthmatic children with influenza A (seasonal or pandemic) had diagnoses of asthma exacerbations compared with those with influenza B (51% vs 29%; P < .01). CONCLUSIONS: The majority of asthmatic children hospitalized with influenza have no additional medical conditions. Complications such as pneumonia and need for intensive care occur in a substantial proportion, highlighting the importance of influenza prevention through vaccination among asthmatic children.

Influenza Vaccination Guidelines and Vaccine Sales in Southeast Asia: 2008-2011

Background Southeast Asia is a region with great potential for the emergence of a pandemic influenza virus. Global efforts to improve influenza surveillance in this region have documented the burden and seasonality of influenza viruses and have informed influenza prevention strategies, but little information exists about influenza vaccination guidelines and vaccine sales. Methods To ascertain the existence of influenza vaccine guidelines and define the scope of vaccine sales, we sent a standard three-page questionnaire to the ten member nations of the Association of Southeast Asian Nations. We also surveyed three multinational manufacturers who supply influenza vaccines in the region. Results Vaccine sales in the private sector were <1000 per 100,000 population in the 10 countries. Five countries reported purchasing vaccine for use in the public sector. In 2011, Thailand had the highest combined reported rate of vaccine sales (10,333 per 100,000). In the 10 countries combined, the rate of private sector sales during 2010–2011 (after the A(H1N1)2009pdm pandemic) exceeded 2008 pre-pandemic levels. Five countries (Indonesia, Malaysia, Singapore, Thailand and Vietnam) had guidelines for influenza vaccination but only two were consistent with global guidelines. Four recommended vaccination for health care workers, four for elderly persons, three for young children, three for persons with underlying disease, and two for pregnant women. Conclusions The rate of vaccine sales in Southeast Asia remains low, but there was a positive impact in sales after the A(H1N1)2009pdm pandemic. Low adherence to global vaccine guidelines suggests that more work is needed in the policy arena.

Burden of Seasonal and Pandemic Influenza-Associated Hospitalization during and after 2009 A(H1N1)pdm09 Pandemic in a Rural Community in India

Background Influenza is vaccine-preventable; however, the burden of severe influenza in India remains unknown. We conducted a population-based study to estimate the incidence of laboratory confirmed influenza-associated hospitalizations in a rural community in western India. Methods We conducted active surveillance for hospitalized patients with acute medical illnesses or acute chronic disease exacerbations in Pune during pandemic and post pandemic periods (May 2009–April 2011). Nasal and throat swabs were tested for influenza viruses. A community health utilization survey estimated the proportion of residents hospitalized with respiratory illness at non-study facilities and was used to adjust incidence estimates from facility-based surveillance. Results Among 9,426 hospitalizations, 3,391 (36%) patients were enrolled; 665 of 3,179 (20.9%) tested positive for influenza. Of 665 influenza positives, 340 (51%) were pandemic A(H1N1)pdm09 and 327 (49%) were seasonal, including A/H3 (16%), A/H1 (3%) and influenza B (30%). The proportion of patients with influenza peaked during August 2009 (39%) and 2010 (42%). The adjusted annual incidence of influenza hospitalizations was 46.8/10,000 during pandemic and 40.5/10,000 during post-pandemic period with comparable incidence of A(H1N1)pdm09 during both periods (18.8 and 20.3, respectively). The incidence of both pH1N1 and seasonal hospitalized influenza disease was highest in the 5–29 year olds. Conclusions We document the previously unrecognized burden of influenza hospitalization in a rural community following the emergence of influenza A(H1N1)pdm09 viruses in India. During peak periods of influenza activity circulation i.e during the monsoon period, 20% of all hospital admissions in the community had influenza positivity. These findings can inform development of influenza prevention and control strategies in India.

Household Transmission of 2009 Pandemic Influenza A (H1N1) and Nonpharmaceutical Interventions among Households of High School Students in San Antonio, Texas

San Antonio, Texas, was one of the first metropolitan areas where 2009 pandemic influenza A (H1N1) virus (pH1N1) was detected. Identification of laboratory-confirmed pH1N1 in 2 students led to a preemptive 8-day closure of their high school. We assessed transmission of pH1N1 and changes in adoption of nonpharmaceutical interventions (NPIs) within households of students attending the affected school. Household secondary attack rates were 3.7% overall and 9.1% among those 0-4 years of age. Widespread adoption of NPIs was reported among household members. Respondents who viewed pH1N1 as very serious were more likely to adopt certain NPIs than were respondents who viewed pH1N1 as not very serious. NPIs may complement influenza vaccine prevention programs or be the only line of defense when pandemic vaccine is unavailable. The 2009 pandemic provided a unique opportunity to study NPIs, and these real-world experiences provide much-needed data to inform pandemic response policy.

Prevalence of 2009 Pandemic Influenza A (H1N1) Virus Antibodies, Tampa Bay Florida — November–December, 2009

Background In 2009, a novel influenza virus (2009 pandemic influenza A (H1N1) virus (pH1N1)) caused significant disease in the United States. Most states, including Florida, experienced a large fall wave of disease from September through November, after which disease activity decreased substantially. We determined the prevalence of antibodies due to the pH1N1 virus in Florida after influenza activity had peaked and estimated the proportion of the population infected with pH1N1 virus during the pandemic. Methods During November-December 2009, we collected leftover serum from a blood bank, a pediatric childrens hospital and a pediatric outpatient clinic in Tampa Bay Florida. Serum was tested for pH1N1 virus antibodies using the hemagglutination-inhibition (HI) assay. HI titers ≥40 were considered seropositive. We adjusted seroprevalence results to account for previously established HI assay specificity and sensitivity and employed a simple statistical model to estimate the proportion of seropositivity due to pH1N1 virus infection and vaccination. Results During the study time period, the overall seroprevalence in Tampa Bay, Florida was 25%, increasing to 30% after adjusting for HI assay sensitivity and specificity. We estimated that 5.9% of the population had vaccine-induced seropositivity while 25% had seropositivity secondary to pH1N1 virus infection. The highest cumulative incidence of pH1N1 virus infection was among children aged 5–17 years (53%) and young adults aged 18–24 years (47%), while adults aged ≥50 years had the lowest cumulative incidence (11–13%) of pH1N1 virus infection. Conclusions After the peak of the fall wave of the pandemic, an estimated one quarter of the Tampa Bay population had been infected with the pH1N1 virus. Consistent with epidemiologic trends observed during the pandemic, the highest burdens of disease were among school-aged children and young adults.

Validity of clinical case definitions for influenza surveillance among hospitalized patients: results from a rural community in North India

Objective:  Clinical case definitions used for influenza surveillance among hospitalized patients vary and need systematic evaluation.