By the end of April 2009, two cases of confirmed novel H1N1 were detected in the United States. 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 2009, 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 H1N1 influenza is a negative-sense RNA virus of the orthomyxoviridae family. 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 7-10 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. Laboratory findings are high CPK, high LDH and lymphopenia [1
]. 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
]. 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). 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. [7
] performed on 97 patients who underwent chest radiography at admission, the most frequent abnormal pattern on radiography was ground glass opacities in the central and middle lung zones, which was followed by consolidation with slightly less frequency. This is in contrast with our findings which showed predominant involvement of the lower lung zones and consolidation as the most common manifestation. 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. Another study reviewed the High Resolution Computed Tomography Scan (HRCT) findings of 18 patients with the new swine flu influenza. 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 their study, patients with high LDH were more likely to have consolidations on HRCT [8
Considering the association of chest findings and patients’ prognosis, it was previously demonstrated that in patients with community acquired pneumonia, bilateral pleural effusion may predict short term mortality [9
]. 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.