Patients Hospitalized with 2009 Pandemic Influenza A (H1N1) --- New York City, May 2009

Patients Hospitalized with 2009 Pandemic Influenza A (H1N1) --- New York City, May 2009

The first cases of 2009 pandemic influenza A (H1N1) in New York City occurred in April 2009, raising many questions about how best to contain the epidemic. To rapidly assess the severity of influenza illness and identify persons at highest risk for severe infection, the New York City (NYC) Department of Health and Mental Hygiene (DOHMH) reviewed the medical charts of the first 99 patients with laboratory confirmed H1N1 admitted to any NYC hospital. The purpose of the review was to characterize the demographics of the first hospitalized patients, identify associated underlying medical conditions, describe the course and severity of disease, and examine the use of antiviral medications. This report summarizes the findings of this analysis. Approximately 60% of admitted patients were aged <18 years. The most commonly documented underlying condition was asthma, observed among 50% of patients aged <18 years and 46% of adult patients. Multiple underlying conditions were observed in 17% of patients (12% of children, 24% of adults). Patients treated with oseltamivir within 2 days of symptom onset had shorter median hospitalizations than those who did not (2 days versus 3 days [p = 0.03]). The findings of this assessment were used to inform immediate outbreak response measures in New York City. During such outbreaks, public education campaigns should encourage patients at high risk of severe illness to seek treatment promptly after symptom onset and should emphasize the importance of early antiviral therapy for patients with underlying risk conditions (1,2).

The subjects of the assessment were the first 99 patients with polymerase chain reaction-confirmed H1N1 influenza admitted to any NYC hospital during April 25--May 24, 2009. To conduct the assessment, DOHMH physicians used a modified abstraction form based on one developed by CDC to collect clinical and laboratory data from paper and electronic medical charts of the hospitalized patients. Reviewing physicians identified underlying conditions known to increase risk for severe influenza (1,2). Body mass index (BMI) was calculated using height and weight recorded in the chart; BMI percentile-for-age for patients aged 2--17 years was determined by using CDC growth charts (3) and the standard formula (4) was used for nonpregnant adults aged ≥18 years. Patients with BMI ≥30 were categorized as obese (4). Wilcoxon ranked-sum tests were conducted to compare median lengths of hospitalization among surviving patients (statistically significant results defined as p< 0.05).

Among the 99 hospitalized patients, 19 (19%) were aged <5 years, 39 (39%) were aged 5--17 years, and nine (9%) were aged ≥50 years. These proportions differed from the proportions for the same age groups in the general population (2007 census projections for New York City), which were 7%, 16%, and 29%, respectively, indicating that hospitalized patients were generally younger than the general population. Of the hospitalized patients, non-Hispanic Asians and whites were underrepresented compared with the NYC general population, and Hispanics were overrepresented (Table 1).

The most common presenting symptoms were fever and cough. A total of 95 patients (96%) had measured or subjective fever on admission; 56 (57%) had measured fever of >100.4°F (median maximum temperature: 102.2°F [39.0°C]; range: 97.0°F --105.9°F [36.1°C--41.1°C]) and 39 (39%) had subjective fever. A total of 89 (90%) reported cough. Additional presenting symptoms reported included runny nose (42%), shortness of breath (34%), headache (33%), vomiting (32%), and myalgias (31%). Elevated heart and respiratory rates for age were observed in 63 (64%) and 48 (48%) of patients, respectively. Abnormally high (20 patients) and low (seven patients) white blood cell counts were observed in 27 patients (27%). A total of 87 patients (88%) received at least one chest radiograph, of which 38 (44%) were read as abnormal. The most common abnormalities were single lower lobe infiltrates (24%), interstitial infiltrates (18%), and multilobar infiltrate (8%). Complications observed during hospitalizations included acute respiratory distress syndrome (ARDS) in three patients (3%), shock in three (3%), sepsis in five (5%), liver impairment in five (5%), and renal failure in five (5%).

Underlying medical conditions known to increase the risk of severe influenza or influenza complications (1,2) were observed in 73 patients (74%), including 37 children (64%) and 36 adults (88%), and 17 patients (17%), including seven children (12%) and 10 adults (24%), had more than one underlying condition (Table 2). The most commonly documented underlying condition was history of asthma, recorded for 29 patients aged <18 years (50%) and 19 adults (46%). Also recorded were chronic metabolic disorders including diabetes (11 patients [11%]), neurological disorders including neuromuscular disorders, seizure disorders, or cognitive dysfunction (10 patients [10%]), and immunosuppressive conditions, including HIV or medication-related conditions (five patients [5%]). Among the 24 female patients aged 15--49 years at the time of hospital admission, seven (29%) were pregnant or within 10 days after delivery, of whom four had additional underlying conditions. Among the 20 adults and 28 patients aged <18 years for whom information was available, 12 adults (60%) and five patients aged <18 years (18%) were obese. Underlying conditions (1,2) were observed in 11 of the obese adults and four of the obese patients aged <18 years.

Among 24 patients (24%) admitted to the intensive care unit (ICU), seven (29%) required mechanical ventilation. Median age of ICU patients was 19 years (range: 0--55 years). Patients admitted to the ICU had longer median lengths of stay (4 days, range: 1--29 days) compared with other hospitalized patients.

Four patients (4%) died. Three of those patients were obese. Underlying conditions among the four included asthma (two) and Down syndrome (one). One patient died on the day of admission, two other patients died within 4 days of admission, and the fourth patient died 41 days after admission.

Median length of time from symptom onset to admission was 2 days (range: 0--14). Among the 95 patients who survived their hospitalization, a difference of 1 day for median length of hospitalization was observed for children compared with adults (2 days [range: 0--20] vs. 3 days [range: 1--29]; p = 0.01).

Antiviral treatment with oseltamivir was received by 76 patients (77%); three (4%) initiated treatment before hospitalization. Of the 76 patients who received antivirals, 36 (47%) began treatment within 2 days of symptom onset. Median time from onset of illness to treatment was 3 days (range: <24 hrs to 15 days). Patients who initiated antiviral treatment within the 2 days recommended by CDC (1) had shorter lengths of stay than those who initiated treatment later (median: 2 days versus 3 days; p = 0.03).

Reported by: ME Slopen, MSW, MC Mosquera, MD, S Balter, MD, BD Kerker, PhD, MA Marx, PhD, MR Pfeiffer, MPH, A Fine, MD, J Eavey, MSPH, TG Harris, PhD, EC Olson, MPH, C Stayton, PhD, C Wu, MPH, EH Lee, MD, New York City Dept of Health and Mental Hygiene.

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Patients Hospitalized with 2009 Pandemic Influenza A (H1N1) --- New York City, May 2009