Severity of Influenza A 2009 (H1N1) Pneumonia Is Underestimated by Routine Prediction Rules. Results from a Prospective, Population-Based Study

Abstract

BackgroundCharacteristics of patients with community-acquired pneumonia (CAP) due to pandemic influenza A 2009 (H1N1) have been inadequately compared to CAP caused by other respiratory pathogens. The performance of prediction rules for CAP during an epidemic with a new infectious agent are unknown.MethodsProspective, population-based study from November 2008–November 2009, in centers representing 70% of hospital beds in Iceland. Patients admitted with CAP underwent evaluation and etiologic testing, including polymerase chain reaction (PCR) for influenza. Data on influenza-like illness in the community and overall hospital admissions were collected. Clinical and laboratory data, including pneumonia severity index (PSI) and CURB-65 of patients with CAP due to H1N1 were compared to those caused by other agents.ResultsOf 338 consecutive and eligible patients 313 (93%) were enrolled. During the pandemic peak, influenza A 2009 (H1N1) patients constituted 38% of admissions due to CAP. These patients were younger, more dyspnoeic and more frequently reported hemoptysis. They had significantly lower severity scores than other patients with CAP (1.23 vs. 1.61, P = .02 for CURB-65, 2.05 vs. 2.87 for PSI, P<.001) and were more likely to require intensive care admission (41% vs. 5%, P<.001) and receive mechanical ventilation (14% vs. 2%, P = .01). Bacterial co-infection was detected in 23% of influenza A 2009 (H1N1) patients with CAP.ConclusionsClinical characteristics of CAP caused by influenza A 2009 (H1N1) differ markedly from CAP caused by other etiologic agents. Commonly used CAP prediction rules often failed to predict admissions to intensive care or need for assisted ventilation in CAP caused by the influenza A 2009 (H1N1) virus, underscoring the importance of clinical acumen under these circumstances.

The frequency of influenza and bacterial coinfection: a systematic review and meta‐analysis

“…The full‐text review resulted in the exclusion of an additional 74 articles. A total of 27 articles encompassing 3215 patients met all the inclusion criteria and were included in the final analysis 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54. Of those 27, only eight studies, with 334 patients, provided the numbers or percentages of each bacterial coinfecting pathogen 28, 32, 33, 34, 38, 43, 46, 47.…”

“…All 27 included studies were observational, of which 13 (1218 patients) were prospective studies,30, 32, 33, 36, 40, 41, 43, 44, 48, 49, 50, 51, 52 and 14 (1997 patients) were retrospective analyses (Table 1). The majority (21) of studies were cohort studies, and the rest were case–control studies.…”

“…Severity of illness varied among studies, but all were focused on hospitalized patients, suggesting a greater than average severity. Eleven of the studies (1007 patients) focused exclusively on patients initially enrolled in an intensive care unit (ICU),32, 34, 35, 38, 39, 41, 42, 44, 46, 47, 51 10 enrolled non‐ICU hospitalized patients (973 patients),30, 33, 36, 37, 40, 43, 45, 49, 53, 54 3 enrolled patients in the emergency department (ED; 135 patients),28, 48, 50 and 2 enrolled patients in a mix of inpatient and outpatient settings (1100 patients) 29, 52. The median sample size was 51 (IQR, 18·5–101), and the mean was 119 (SD: 203), which was driven by three large studies29, 44, 53 that contributed 1958 (61%) of the total number of patients included in this analysis.…”

Clinical characteristics of 75 pandemic H1N1 influenza patientsfrom Turkey; risk factors for fatality

“…The patients with influenza-like illnesses were admitted to health care units and cough, headache, and fatigue were the prominent symptoms, especially among young adults. However, pneumonia patients that were hospitalized in the clinics or intensive care units (ICUs) were generally infants or adults older than 65 years of age (1)(2)(3). For all that, severe H 1 N 1 pneumonia also affected some young adults without any underlying comorbidities in both the United States and Turkey (4).…”

“…Serum D-dimer values may increase in inflammatory conditions, such as pneumonia, sepsis, and septic shock (3,8). We hypothesized that D-dimer levels might be used as an assessment tool to evaluate the severity of pneumonia.…”