Our study population was obtained from our database throughout the year of 2016; however,
all patients selected had the H1N1 infection diagnosed between the three months before winter in the south hemisphere,
which configured an atypical and early outbreak of H1N1 infection.[11]
The major clinical findings among our population were flu-like symptoms (97.9%) as expected for a respiratory infection.[12] DM,
systemic hypertension,
dyspnea,
thoracic pain, temperature and CRP levels were the clinical features associated with worse clinical outcomes. Moreover,
the radiological findings were the presence of pulmonary infiltrate,
consolidation,
and pleural effusion on CR,
presence of GGO and consolidation on CT,
and diffuse pattern of imaging abnormality on CT or CR.
In the logistic regression,
the presence of DM,
thoracic pain, levels of body temperature,
an alteration on CR or CT,
diffuse pattern of distribution of any abnormality on CR or CT; pulmonary infiltrate on CR,
GGO on CT,
and pleural effusion on CT or CR were the variables that predicted worse clinical outcomes.
In the hierarchical cluster analysis,
the cluster that better correlated with worse clinical outcomes contained GGO on CT, pulmonary infiltrate on CR,
consolidation and distribution on CT or CR.
Regarding the clinical features,
our results are in line with similar studies that evaluated symptoms associated with a worse outcome,
as they demonstrated that fever and dyspnea may predict hospitalization.[12] Studies that have analyzed only patients with severe H1N1 admitted to an ICU have also demonstrated that symptoms were similar to typical seasonal H1N1,
such as cough,
dyspnea,
fever,
myalgia and headache.[1] The results are also comparable to studies that have analyzed mild and severe infections.[7]
Our study also demonstrated chest pain as a predictor of worse outcome,
a feature that was not found in previous studies and may be related to the institution sample or type of H1N1 virus.
Therefore,
despite minor differences among studies,
H1N1 infection exhibits similar clinical features that predict severity over the years regardless of the genotype.
In contrast to previous studies,
we did not identify death due to H1N1 infection.
The average mortality among adult patients in the United States was 26%.[13]
With regards to imaging features,
the CR and CT findings in our study population are comparable to the most representative studies over the years since the first H1N1 outbreak in 2009.[5,
12,
14] All 37 patients with worse outcomes had at least a pulmonary abnormality in an imaging exam,
and we identified significant differences among the groups with and without hospitalization.
The imaging features detected in our population are in line with previous data of viral pneumonia,
including pulmonary infiltrate,
GGO,
consolidation and pleural effusion.[10,
15] Comparable to other studies,
we found that diffuse distribution on an imaging abnormality was associated with worse clinical outcomes.[5,
12,
14]
The clinical relevance of our results essentially relies on the management of patients with H1N1 infection.
Informing the multidisciplinary team of the potential for a worse clinical outcome based on easily accessible information,
such as the presence of DM,
thoracic pain,
body temperature,
and an abnormality on CR or CT,
may add value in the setting of emergency departments.
If clinicians know in advance the possibility of a worse outcome,
they may consider a closer evaluation,
and the emergency discharge decision may be postponed.
This type of guidance may be valuable,
particularly at noncomprehensive centers and during epidemic situations.
There are several potential limitations of this study.
First,
it is a single-center retrospective study,
which is thus subjected to selection bias.
Second,
the study population seemed to have a milder infection than previous studies.
No deaths or sepsis at admission were found,
and 92.9% of the chest CRs were normal.
These results may be related to the earlier outbreak of 2016 in the early autumn or with a less severe H1N1 genotype.
Although our study population was relatively large compared to other imaging studies,
a larger sample would have resulted in a greater generalizability of our imaging findings,
particularly for patients admitted to the ICU.
Consequently,
further studies,
particularly prospective cohorts,
are necessary to overcome these limitations and provide a better generalization of our results.
In conclusion,
our study demonstrates that the presence of DM,
hypertension,
dyspnea, thoracic pain,
or an abnormal CR or CT on admission were associated with worse clinical outcomes in patients with H1N1 influenza A virus infection.
Consolidation and ground glass opacities on CT were also associated with the clinical severity in these patients.
Thus,
the use of readily accessible clinical and imaging features on admission may have a role in the evaluation of patients with H1N1 infection.