The institutional review board approved this retrospective study and waived the requirement for informed consent.
The database from our institution was searched for consecutive patients with a diagnosis of influenza A H1N1 in 2016 as assessed via the upper airway by nasopharyngeal swabbing or a washing test with polymerase chain reaction.
The inclusion criteria were a positive test for influenza A H1N1 and chest radiograph (CR) and/or chest computed tomography (CT) within 48hours before or after the positive test.
The exclusion criteria were another confirmed concomitant pulmonary infection and the absence of follow-up data in the medical records.
Clinical and laboratorial data were obtained from a detailed medical record review conducted by two radiologists with 2 and 3 years of experience,
using a standardized form.
The following clinical data of the patients were assessed: gender,
age,
symptoms at admission (such as flu-like symptoms,
dyspnea,
thoracic pain,
hemoptysis,
and sepsis),
and presence of comorbidities (including systemic hypertension,
diabetes mellitus [DM],
tobacco smoke,
asthma, chronic obstructive pulmonary disease [COPD],
and immunodeficiency).
Information regarding the physical examination at admission was also evaluated,
including the heart rate (HR), temperature,
oxygen saturation (O2),
and blood pressure (BP).
Regarding the laboratory data,
the white blood count,
lymphocytes,
and C-reactive protein (CRP) obtained at admission were assessed.
The CR were performed in posteroanterior and lateral incidences during maximal inspiration with the following parameters: 70-120kV and 1-10mAS.
CT scans were performed on a dual-source 256 row or a 128 row detector CT system. The acquisition parameters were the same for both devices as follows: 115–160mAs; 120kVp; tube rotation time 0,5s; pitch 1,2; and field of view (FOV),
400–430mm.
When contrast was required,
it was performed with 1,0-1,5ml/kg injected at a flow rate of 4,0–5,5ml/s-1.
Images were reconstructed in the axial view using a slice thickness of 1mm and an increment of 0,7mm.
Two board-certificated chest radiologists blinded to the clinical data independently reviewed the radiological exams and analyzed the imaging features according to the Fleischner Society glossary.[9] Figures 1 and 2 exemplifies the imaging features.
The following imaging features were evaluated on CR: pulmonary infiltrate,
consolidation,
and pleural effusion.[10] The distribution of the features was defined as follows: none,
one field,
two fields unilateral,
three or more fields bilateral,
and diffuse.
The following imaging features were assessed on CT: ground glass opacity (GGO), consolidation,
bronchial wall thickening,
and pleural effusion.
The distribution of the imaging features on CT was defined as indicated for CR.
The patients were classified into two groups: good clinical outcome and worse clinical outcome.
A good clinical outcome was defined as hospital discharge after evaluation in the emergency department without the need for hospitalization.
Patients who were hospitalized, admitted to the intensive care unit (ICU) or died were determined to have a worse clinical outcome.
Statistical Analysis
Continuous variables were tested for normality with the Kolmogorov-Smimov and Shapiro Wilk tests.
The values are expressed as median and percentiles 25 and 75 or as the mean and standard deviation for parametric and non-parametric data respectively.
The categorical data are presented as absolute values and percentages and were tested using Pearson χ2 test and Fisher exact test,
if applicable.
The Mc’Nemar test was used by compare two methods.
Nonparametric data was compared using the Mann-Whitney U test for two independent samples.
The logistic regression models included calculations of corresponding crude and adjusted odds ratios (ORs) and 95% confidence intervals (CI).
Two-tailed p-values ≤0.05 were considered significant.
Hierarchical cluster analysis was performed to identify individual similarities in the diagnostic model through analysis of clusters to try to determine from each of the groups to which they belong.
Statistical significance was considered with p≤0,05.