During our peak pH1N1 season, 1,438 RVP samples were collected. Of these, 1192 were from inpatients (340 samples in patients <5 years, 240 samples 5–18 years, and 612 samples >19 years). Six-hundred and fifteen patients with positive results were included in the final analysis () with a mean age of 20 years (range: 0–97 years). Forty-seven percent of patients had pH1N1 and 53% had another respiratory virus with rhinovirus being the second most prevalent in the population analyzed (34%, ). Fewer patients with pH1N1 were under the age of five years compared to those with other viruses and individuals with pH1N1 were less likely to have cardiac co-morbidities, malignancy, or be admitted from a nursing home. Individuals with pH1N1 were more likely to report a sick contact or to use tobacco.
Characteristics and demographics of patients presenting with pandemic influenza A (pH1N1) compared to other respiratory viruses.
Individuals with pH1N1 were more likely to present with the following symptoms when compared to those with other respiratory viruses: subjective fever or chills, sore throat, nausea, vomiting, abdominal pain, weakness, fatigue, headache, myalgias, and chest pain. Patients with other respiratory viruses were more likely to present with changes in mental status including dizziness or lethargy ().
Signs and symptoms of patients with pandemic 2009 influenza A (pH1N1) compared to other respiratory viruses.
On presentation to the emergency room, patients with pH1N1 exhibited a higher maximum temperature, lower maximum heart rate, respiratory rate, systolic blood pressure, and oxygen saturation (). Patients with pH1N1 were more likely to have lower white blood counts, platelet counts, and potassium levels. Alternatively, patients with pH1N1 were more likely to have higher hemoglobin/hematocrit and albumin levels.
Clinical characteristics of patients with pandemic influenza A (pH1N1) compared to other respiratory viruses.
Of the 529 patients who received a chest radiograph, a greater number of patients with pH1N1 had no acute findings compared to other respiratory viruses (). Other respiratory viruses were more likely to have an interstitial opacity consistent with viral infection on chest radiograph. Thirty percent (161/529) of patients with a chest radiograph had focal or multi-focal airspace findings.
Chest radiograph characteristics of patients with pandemic influenza A (pH1N1) compared to other respiratory viruses.
Most patients with pH1N1 (79.0%) received oseltamivir. More than half received antibacterial agents, and one-third received steroids (). Of the total cohort, only 9.6% had a sputum sample of which 27% were positive for a potential pathogenic microorganism. Forty-four percent (157/357) of patients with no evidence of acute disease or interstitial opacities indicative of viral infection on chest radiograph received antibacterial agents. Forty-six percent of the total cohort had blood sent for culture during their hospitalization, of which 2.5% grew a potential pathogenic microbe (i.e., coagulase-negative staphylococci and other potential skin contaminants were excluded). Twelve percent of the total cohort had a Legionella urine antigen test performed and all were negative.
Treatment and outcomes of patients with pandemic influenza A (pH1N1) compared to other respiratory viruses.
There was no difference between patients infected with pH1N1 or another respiratory viruses regarding admission to an intensive care unit, use of pressors or requirement for intubation (). However, individuals with pH1N1 were more likely to require bilevel positive airway pressure ventilation. Individuals with other respiratory viruses were more likely to receive inhaled bronchodilators or nebulizer therapy in the emergency department. Seven patients (1.1%) in the cohort died and these individuals were more likely to be infected with pH1N1 (2.1% vs. 0.3%, p<0.05).
In patients with cough, the presence of subjective fever/chills independently increased the likelihood of pH1N1 infection (). In patients with cough and gastrointestinal complaints, subjective fever/chills independently increased the likelihood of having pH1N1. Using fever alone did not raise the likelihood of having influenza infection versus another respiratory virus. Using age as a covariate, patients 19 to 59 years of age had the highest likelihood of presenting with pH1N1 compared to other age groups.
Likelihood of patients with clinical characteristics having pandemic 2009 influenza A (pH1N1) using multiple logistic regressions.
An age-adjusted analysis was performed to assess if any factors were found that significantly impacted the likelihood of patients presenting with pH1N1. Age was a significant variable for those patients who had cancer (<5 years OR 5.7, 95% CI 0.51–63.6; 5–18 years OR 0.26, 95% CI 0.023–3.0; 19 and older OR 0.11, 95% CI 0.041–0.31), neurological symptoms (<5 years OR 2.67, 95% CI 0.98–7.3; 5–18 years OR 1.27, 95% CI 0.51–3.17; 19 and older OR 0.52 95% CI 0.23–1.17), or dyspnea (<5 years OR 0.33, 95% CI 0.18–0.61; 5–18 years OR 0.26, 95% CI 0.29–1.21; 19 and older OR 0.95, 95% CI 0.56–1.60). Age was also found to have a significant affect on sodium, creatinine, hematocrit, heart rate, diastolic blood pressure, the use of nebulizers, and the administration of antibiotics across different age groups (<5 years, 5–18 years, and 19 years and older). Patients with pH1N1 who were younger tended to be given more antibiotics (<5 years OR 1.30, 95% CI 0.73–2.33; 5–18 years OR 1.63, 95% CI 0.82–3.2; 19 and older OR 0.42, 95% CI 0.24–0.74). Age did not have a significant impact on any other variables.