Discussion
Influenza can cause signs and symptoms that are indistinguishable from
some severe cases of the seasonal common cold. In general, a chest X-ray
is the first paraclinical test that is performed for the assessment of
respiratory involvement in patients with influenza. In the conditions
that the chest X-ray shows the presence of questionable findings of
respiratory involvement, a chest CT is requested. Also, it has been
suggested that the chest CT is useful in evaluating complications or
evidence of mixed infection, but this issue is open to discussion. So
far, some studies have investigated the radiological features of
influenza patients, especially in A-H1N1 cases. Marchiori et al. (2011)
described the high-resolution CT features of fatal cases of influenza
A-H1N1 virus-associated pneumonia 13. The predominant
findings included areas of airspace consolidation and ground-glass
opacities. Nicolini and co-workers (2011) reported unilateral or
bilateral multifocal ground-glass opacities as the predominant feature
in chest CTs obtained from influenza patients 14. In
another study performed by Agarwal et al. (2009), patchy consolidations
in the lower and central lung zones were reported as the main
characteristic of A-H1N1 subjects 15. Also, Ajlan et
al. (2009) stated that unilateral or bilateral ground-glass opacities
with or without associated focal or multifocal areas of consolidation
are the crucial parameters that should be considered in influenza
patients 16.
In our study, the rate of patchy infiltration detection, as a crucial
parameter, was significantly different between the three types of
investigated influenza strains (P<0.05). Patchy infiltration
is considered as a poorly defined area of lung consolidation with
scattered opacification seen on chest imaging. This clinical
characteristic has been reported in many studies performed on the
influenza disease. Rostami et al. (2011) studied the radiological
characteristics of influenza A-H1N1 patients 17. In
their survey performed in the Isfahan city of Iran, patchy infiltration
was one of the most common thoracic CT findings in pandemic H1N1. The
results of the present study are in agreement with the results of
Rostami’s study. In another study, Elicker and co-workers (2010)
reported the thoracic CT findings of novel influenza A-H1N1 infection in
immunocompromised patients 18. In their study, some
patients had atypical CT findings including focal lobar consolidation
and patchy lower lobe consolidation with soft tissue centrilobular
nodules. Such atypical findings may be indicative of a compromised
immune status.
To date, a number of studies have reported the clinical features of
various types of influenza, especially the A-H1N1 subtype. Walsh et al.
(2002) described the clinical features of influenza-A infection in older
hospitalized subjects 19. They stated that the
presence of cough, fever, and severe illness are valuable in opting for
respiratory isolation and designing antiviral trials for influenza
patients. In 2009, Cao and co-workers listed the clinical features of
influenza A-H1N1 patients 20. Based on their report,
the most common symptoms of A-H1N1 influenza patients were fever and
cough, which occurred in 67.4% and 69.5% of cases, respectively. In
another survey, Hu et al. (2003) surveyed the clinical features of
influenza A and B in younger patients and its association with myositis21. These researchers reported fever, cough, and
rhinorrhea as the most common clinical manifestations, with benign acute
childhood myositis being present in 5.5% and 33.9% of the type A and B
patients, respectively. Irving and his colleagues (2011) conducted a
study for the comparison of clinical manifestations of medically
attended influenza-A and influenza-B in defined subjects over four
seasons 10. They concluded that over four influenza
seasons, clinical signs and symptoms were alike for cases with
predominantly outpatient-attended influenza-A and influenza-B virus
infections.
As previously mentioned, fever seems to be the most common influenza
manifestation; Calitri et al. (2010), in their cross-sectional study,
confirmed this among 2009 H1N1 influenza patients 22.
In another study, Plessa et al. (2010) declared that fever was the most
common symptom in pediatric patients with H1N1 influenza23. In our cross-sectional study, fever was present in
most patients with various types of influenza. Notably, the fever
temperature was significantly higher among influenza A-H3N2 subjects
than A-H1N1 and B-H1N1 subjects (P<0.05). Kaji and co-workers
(2003) investigated the differences in clinical features between A-H3N2,
A-H1N1, and B influenza subjects in Japan 24. They
reported that A-H3N2 influenza was more severe than A-H1N1 or B in terms
of fever, leukopenia, and CRP level elevation. Our finding related to
fever is in agreement with the Kaji et al. study.
Dynamic determination of inflammatory agents may offer important
insights into individual alterations in the control of inflammation and
risk for disorders. The CRP is produced by the liver in response to
signaling by pro-inflammatory cytokines. A high level of plasma CRP is a
marker of inflammation associated with a wide variety of disorders
ranging from infection to malignancy 25,26. In recent
years, the CRP level in patients with influenza has been of interest to
researchers. Morton et al. (2017) suggested that CRP is a crucial
parameter for determining the admission, observation, or discharge of
H1N1 influenza patients 27. Based on their work, the
CRP determinant was the most important predictor of safe discharge. In
another survey, Li and co-workers found that CRP levels could indicate
which febrile children under three months of age should undertake blood
culture tests during influenza seasons 28. In the
present study, we reported a significant difference between the levels
of CRP in the three groups of influenza patients (P<0.05). Our
results are consistent with those of Kaji et al., who reported a
meaningful difference in CRP levels between A-H3N2, A-H1N1, and B
influenza subjects in Japan.
For a probable diagnosis of influenza, many non-specific serological
parameters have been suggested, such as lymphopenia, monocytosis,
thrombocytopenia, and leukocytosis or leukopenia. The WBC count is one
of the parameters that has frequently been investigated. In a survey of
hospitalized subjects with A-H1N1 influenza during the first two months
of its pandemic, leukopenia was observed in 20% of patients. Wiwanitkit
et al. (2013) presented leukopenia and lymphopenia as important findings
of influenza that can be verified through blood tests29. Soleimani and co-workers reported that the
presentation of influenza in children is variable and A-H1N1 influenza
may cause leucopenia and thrombocytopenia 30. As
previously mentioned, Kaji et al (2003) reported that influenza A-H3N2
was more severe than A-H1N1 or B in terms of leukopenia24. In contrast, we did not find any meaningful
difference between the numbers of WBC in the three groups under study.
This retrospective study was confronted with some limitations. Firstly,
despite the use of the RT-PCR molecular technique for the definitive
diagnosis of the influenza subtype, some of the features seen on CT
scans could have been consequences of infections other than influenza. A
second limitation was the lack of access to pathological samples of the
patients’ lungs. As we know, the correlation between radiological and
histopathological findings is a considerable issue in influenza.
Finally, our study featured a relatively low number of patients,
limiting its power.