Radiology of Influenza A (H1N1)

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Of our patients, Eight The abnormal pattern was unilateral in four Other findings included cardiomegaly in five The platelet count was low in Hb was low in White blood cell WBC was high in Twelve patients with a mean age of Seven had a predisposing condition three cardiovascular disease, two respiratory disease, one immunodeficiency, one cancer, three others. Four patients died. Four These patients were resistant to rimantadine and amantadine and had no contact with swine. Further cases of the new swine flu were identified in Mexico and other countries.

By June , several confirmed cases were reported from 74 countries and the virus was known to have human-human transmission and by that time WHO raised the alert level to phase 6 which is the pandemic level [ 5 ]. The center for disease control and prevention CDC recognizes it with an influenza like syndrome presenting with high fever, cough or sore throat.

Its diagnosis is confirmed by real-time reverse transcription polymerase chain reaction PCR or viral culture. Its incubation period is between 1 and 7 days. The patients are thought to be contagious from one day before to days after the onset of the disease. Patients with a background disease including respiratory tract and heart disease are more likely to require hospitalization. The clinical presentations have been reported as fever, headache, sore throat, dyspnea, diarrhea and rhinorrhea.

The new swine flu influenza S-OIV is known to be susceptible to neuraminidase inhibitors and there is recommendation to give oseltamivir as prophylaxis to the high risk group [ 2 ]. Different radiologic manifestations have been reported in several studies of the new swine flu influenza virus [ 4 ][ 6 ]. Perez Pallida [ 1 ] reported the radiologic manifestations of 18 patients with documented H1N1 infection as bilateral alveolar opacities which are predominantly basal and other observations being interstitial opacities including linear and reticular.

Bibliographic Information

In a study on 66 patients, the most common abnormal pattern was consolidation most commonly observed in the lower and central lung zones and patients admitted to the ICU were more likely to have three or more lung zones involved [ 4 ]. This result was consistent with our study. The patients were more likely to have consolidations in the lower lung fields and those admitted to the ICU having two or more lung fields involved; however, in another study by Aviram et al. This is in contrast with our findings which showed predominant involvement of the lower lung zones and consolidation as the most common manifestation.

Chest imaging in H1N1 influenza

In their study, patients with bilateral and peripheral involvement or four or more lung zone involvement were more likely to have severe outcome, which is in consistence with our findings in patients admitted to ICU. It should be noted that our study population included patients with a more severe presentation and was not a sample of the population diagnosed with H1N1 and the results may only be interpreted in the setting where the manifestation is more severe and not the entire population of patients diagnosed with H1N1. In this study, the abnormal pattern was most commonly the ground glass opacity present in the peripheral region which is consistent with our results.

In our group of patients, bilateral pleural effusion was not a predictor of mortality. Interestingly, in another report of patients with acute respiratory distress syndrome, involvement of more than two lung zones has been associated with the worst outcome [ 10 ]. In our group of patients, we also found that those who were admitted to the ICU were more likely to have more than two lung zones involved.

Detection of multiple consolidations on radiography may represent a severe viral infection or superimposed bacterial infection which would necessitate antibiotic and some advocate administration of antibiotic to patients suspected of H1N1 and radiologic manifestation of extensive involvement or consolidation. In our group of patients, those with severe presentation were also receiving antibiotic alongside oseltamivir. In conclusion, we found our experience with our group of patients with H1N1 influenza consistent with previous reports as consolidation on the lower lung fields being most common on radiography and ground glass opacities most common on the CT scan.

Becoming familiar with the clinical and radiographic presentations of this very infectious disease helps in early diagnosis, treatment and isolation of patients. These findings may help early detection and treatment of this disease during the period of high prevalence.

Iran J Radiol. DOI: Financial Disclosure: None declared. National Center for Biotechnology Information , U. Journal List Iran J Radiol v. Published online Dec Author information Article notes Copyright and License information Disclaimer. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Objectives The aim of this study was to evaluate the imaging findings of patients with documented H1N1 infection referred to our center.

Patients and Methods Thirty-one patients 16 men with documented H1N1 infection were included in our study. Results The mean age was Conclusions In patients with the novel swine flu infection, the most common radiographic abnormality observed was consolidation in the lower lung zones. Background The new H1N1 influenza infection or the swine flu is a very contagious respiratory tract infection which came to attention in Mexico in April [ 1 ].

Objectives In this study, we reviewed the radiologic manifestations in patients with documented H1N1 infection who were admitted to Masih Daneshvari Hospital to obtain the characteristic radiologic findings of H1N1 infection in Iran and to find any difference with previous studies if present. Patients and Methods In this retrospective study, the files of 54 patients admitted to Masih Daneshvari Hospital a referral hospital for respiratory tract infection and diseases , from November 1 to December 30 , who had the criteria for H1N1 infection determined by US Centers of Disease Control and Prevention were reviewed.

Radiologic Evaluation Twenty eight patients had postero-anterior and lateral radiographs, of which three were anteroposterior portable bedside radiographs. Image Analysis One experienced radiologist in the field of thoracic imaging examined the radiographs. Table 1 Patients Background Disease. Co-existing Condition No.

Imaging swine flu: is it ever necessary?

Respiratory disease Asthma, COPD a 8 Cardiovascular ischemic heart disease, hypertension 5 Immunodeficiency common variable immunodeficiency, HIV 2 Cancer multiple myeloma, synovial cell cancer 2 Others addiction, suicide, convulsions 4. Open in a separate window. Figure 1. A year-old female with respiratory symptoms and confirmed H1N1 infection. Chest x-ray shows extensive bilateral air-space opacities mainly in the lower zones.

Figure 2. A year-old female with respiratory symptoms and proved H1N1 infection. Virus-specific imaging with PET or SPECT might make use of a radiolabeled probe that binds with high affinity to a virus-specific molecule, or is selectively modified by a virus-encoded enzyme, causing it to be retained within infected cells. SPECT and PET are based on the selective retention of radiotracers molecules at sites of biological interest through a broad range of mechanisms including either as a result of high-affinity binding to a chosen molecular target or through trapping in cells by mechanism pathways such as modification by a specific enzyme.

By using highly energetic photons of a single frequency, PET reduces soft-tissue attenuation, scatter, and noise. However, a limiting factor in PET resolution is the distance that the positron must travel through tissues before undergoing annihilation. In contrast, the various radiotracers used for SPECT imaging release single photons, with a range of energies depending on the decay characteristics of the radionuclide. Although SPECT has traditionally been considered to be less quantitative and more subject to soft-tissue attenuation than PET, its use for infectious disease research is being enhanced by improved collimation, the use of CT for attenuation correction, and evolving quantitative techniques.

Moreover, as a cross-sectional technique, SPECT provides significant advantages over planar nuclear medicine imaging for locating sites of disease. For example, whole antibodies or antibody fragments labeled with 99m Technetium or Indium can be imaged with SPECT for a broad range of potential infectious disease applications.

Iranian Journal of Radiology - Imaging Findings in Patients With H1N1 Influenza A Infection

Because deoxyglucose is taken up by cells and phosphorylated but not further metabolized, the radiotracer is selectively trapped in cells with high rates of glycolysis. FDG - PET imaging has a flourishing oncologic literature, based on the detection of active neoplasms with elevated glycolysis by combining PET with CT, which has greater sensitivity and specificity than either method alone. For example, FDG has been used to visualize the response to the introduction of endotoxin into the lungs of human volunteers Figure 6 [ 39 , 40 ].

This suggests that FDG - PET could be particularly useful for imaging the inflammatory response to severe respiratory viral infections, because studies of human cases and experimental models in mice and ferrets indicate that acute inflammatory responses play a critical role in the severe respiratory dysfunction induced by the H1N1 and the H5N1 avian influenza viruses and by the SARS coronavirus [ 19 , 41—46 ]. Radionuclide imaging of experimental influenza or SARS coronavirus infections could help to resolve the question of whether anti-inflammatory therapies are beneficial or harmful for these conditions [ 47—51 ].

CT upper row and 18 FDG-PET images of the lungs of a human volunteer before and 24 hours after an intrabronchial installation of endotoxin. The subtraction image shows an area of tracer retention representing an acute inflammatory response. Red indicates the highest and blue the lowest level of activity.

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From [ 39 ], with permission. The same authors have also found that, in patients with acute lung injury and ARDS from causes other than viral infection, the metabolic rate of pulmonary tissues is markedly increased, even when CT shows them to be normally aerated [ 53 ]. This work suggests that FDG - PET quantitation of inflammation in infected animals could be experimentally compared with measurements of viral replication, cellular markers, and gene expression to identify relationships among these factors and pulmonary parenchymal injury.

The PET image shows increased glucose metabolism, both in areas that contain infiltrates by CT and in regions of apparently normal aeration. Red indicates the highest and blue the lowest level of radiotracer activity. Courtesy of Giacomo Bellani. Because intravenously administered FDG is taken up and trapped nonspecifically by a wide range of white blood cells, efforts are under way to label specific populations of white blood cells in vitro.

In the case of acute infection, in vitro labeling of neutrophils could be a useful method of tracking host responses [ 24 , 54 ]. For example, a 64 Cu-labeled peptide that targets the formyl peptide receptor on neutrophils has been used to image bacterial infections in mice [ 55 ]. Key issues include demonstrating the stability of the neutrophil-peptide complex, which affects the localization of a molecular process if the radioactive molecule fails to remain attached to the target peptide, and studying the effect on tracer uptake of increased perfusion in areas of infection [ 55 ].

Because the techniques just described cannot reliably distinguish between infection and other inflammatory processes, there is a need for methods that could specifically detect viral replication and track the spread of a pathogen in the respiratory tract.

One possible approach would be to design radiolabeled probes that bind with high affinity to virus-encoded molecules or that are substrates for a virus-encoded enzyme Table 2. An example of the latter is the herpesviral TK, which phosphorylates thymidine analogues that are not substrates for the host enzyme. Compounds, such as acyclovir and its analogues, can therefore be used both as antiviral drugs for the treatment of herpesviral infections and as radiolabeled tracers to detect sites of replication or recombinant TK expression [ 56 ].

The method has been used to image experimental herpesviral infections of tumors, but its use for visualizing herpesviral encephalitis has been limited by the requirement for the probe to penetrate the blood-brain barrier [ 57—59 ]. The published literature has not yet established the use of radiolabeled antiviral drugs as probes to image influenza or SARS, but opportunities might exist to use amantadine and rimantadine, which inhibit influenza viral replication by selectively occupying the M2 ion channel; oseltamivir and zanamivir, which bind to the active site of the influenza neuraminidase; and experimental drugs that inhibit the SARS coronavirus protease as imaging agents [ 34 , 36 ].

PET has been used to image the distribution of radiolabeled oseltamivir in uninfected mice and of inhaled zanamivir in healthy human volunteers [ 60 , 61 ]. It is interesting to speculate that these radiolabeled drugs could also be used to identify the distribution of influenza virus in the respiratory tract of patients with influenza, unless their distribution would essentially localize nonspecifically to areas of increased perfusion, as has been observed for radiolabeled ciprofloxacin in experimental bacterial infections [ 62 ].

In MRI, exposure of the body to a combination of a strong magnetic field and pulses of radio-frequency energy induces signals that reflect the local molecular environment. In addition to providing detailed structural images, MRI can obtain information on physiologic processes through the use of contrast agents, such as superparamagnetic iron oxide SPIO particles, to label immune cells and the analysis of spectral data to detect and quantify specific substances in tissues.

However, technical innovations, such as respiratory gating and adjusted MRI sequences, are addressing these challenges to image pulmonary infections [ 64—66 ]. MRI is now being used to track the development of pulmonary lesions and characterize inflammatory responses in murine models of bacterial infection Figure 8A [ 67—70 ]. Although MRI has been used to study the effects of influenza on the central nervous system and the heart, it has yet to be applied in published research on pulmonary influenza or other respiratory viral infections. However, advances in pulmonary MRI and MRI-compatible cell labeling are providing a unique opportunity for these studies.


For example, inflammatory cells loaded ex vivo with antiviral drugs or nanoparticles have been demonstrated to localize to sites of infection [ 71 , 72 ]. SPIO particles, which cause local magnetic susceptibility artifacts, are particularly useful for studying inflammatory processes, because they are detectible as dark hypointense regions much larger than the particles themselves, rendering them visible even when only a few cells are labeled Figure 8B [ 73 ].

Although promising for identifying areas of inflammation in solid organs, such as the brain, these methods may prove to be less useful for studying respiratory tract infections, because dark areas of diminished signal intensity at sites of SPIO particle uptake may resemble normal lung. Identification by MRI of areas of inflammation in the lungs of a mouse 24 and 48 hours after an intratracheal inoculation of lipopolysaccharides, based on the uptake of 19 F-labeled emulsified perfluorocarbons, which are phagocytized by monocytes and macrophages.

Public Service announcement on Influenza A (H1N1)

A and B , 1 H gradient echo images of the thorax. D , Superimposed images, with sites of perfluorocarbon uptake highlighted in red. From [ 67 ], with permission. Because it uses relatively inexpensive detection equipment and does not involve radioactivity, BLI is the molecular imaging method most accessible to bench researchers.

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