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Original Report |
1 Department of Medical Imaging, St. Michael's Hospital, 60 Bond St., Toronto,
ON M5B 1W8, Canada.
2 Department of Medical Imaging, University of Toronto, Faculty of Medicine,
Fitzgerald Building, 150 College St., Rm. 127, Toronto, ON M5S 3E2,
Canada.
3 Department of Respiratory Medicine, West Park Health Centre, 82 Buttonwood
Ave., Toronto, ON M6M 2J5, Canada.
4 Department of Microbiology, Mount Sinai Hospital, 600 University Ave.,
Toronto, ON M5G 1X5, Canada.
Received May 21, 2003;
accepted after revision July 8, 2003.
Address correspondence to R. Bitar
(richard.bitar{at}utoronto.ca).
Abstract
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CONCLUSION. The study group was composed of 13 patients from a single institution. Three distinct chest radiographic patterns were observed: focal peripheral air-space disease at presentation with gradual resolution (most common pattern, 10/13 patients), normal findings on chest radiography at presentation followed by focal air-space disease (2/13 patients), and normal findings on chest radiography at presentation followed by a "round" pneumonia pattern (1/13 patients). There was no evidence of pleural reaction, lymphadenopathy, or interstitial changes.
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It is believed that the mechanism of transmission of SARS is by droplet secretions or by direct or indirect person-to-person contact from a person who has SARS [2, 4–6]. Although the etiologic cause remains unknown, the ease of the spread of SARS and its short incubation period (2–12 days) suggest a viral source for the causative agent. Recent reports in the literature suggest a novel member of the coronavirus family, tentatively named the Urbani SARS-associated coronavirus, as the causative agent [7, 8].
SARS is associated with significant morbidity and mortality. Although some patients with SARS only experience a febrile respiratory disease, a variety of patients have progressed to respiratory failure, requiring admission to ICUs, intubation, and ventilatory support. In some patients, SARS is the cause of death [2, 4–6]. As of July 2003, the WHO reported 812 deaths from SARS, representing 9.6% of the reported cases worldwide.
According to the WHO and the Centers for Disease Control and Prevention (CDC) [9, 10], a suspect case of SARS is diagnosed in any person presenting after November 1, 2002, with a history of a fever greater than 38°C (100.4°F); respiratory symptoms including coughing or difficulty breathing; a history of close contact with a suspected or probable case of SARS; or a history of travel to or residence in a SARS-affected area. A probable case of SARS is a suspected case with evidence of pneumonia or respiratory distress syndrome on chest radiography, or any suspect case with autopsy findings consistent with the pathology of respiratory distress syndrome without an otherwise-identifiable cause.
Although the definition of a probable case of SARS involves chest radiographic findings of pneumonia or respiratory distress syndrome, the precise chest radiographic appearance of SARS has only now started to be described in the radiologic literature, with sparse reports appearing in the clinical literature [2, 5, 6, 11].
Health care workers are at a higher risk for contracting the disease than the general public because of the nature of their work environment. Due to the rapid increase in the reported SARS cases in health care workers, we were motivated to review the chest radiographic manifestations of SARS in this particular population. The purpose of this study was to describe the chest radiographic manifestations of SARS in previously uninfected health care workers during the early stages of an outbreak in Toronto, Canada.
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Our patients remained in the hospital for an average of 14 days (range, 12–16 days). The patients were all health care workers whose exposure had occurred very early in the outbreak—before SARS was recognized and before infection control measures were implemented at their workplaces. All patients were treated from the time of admission with IV ribavirin (range, 3–5 days) and broad-spectrum antibiotics. Eight patients exhibited more severe radiologic and clinical abnormalities and also received corticosteroids. All patients improved clinically and were discharged from the hospital.
Portable frontal upright chest radiographs were obtained on the day of admission and daily until discharge. Chest radiographs were also obtained in six of our patients 1 week after their discharge and before being seen in a follow-up clinic. A total of 144 chest radiographs were independently examined by two radiologists with expertise in thoracic imaging from our institution. The chest radiographs were assessed for the presence of interstitial disease, air-space disease, airways disease, nodules, cavities, lymphadenopathy, and pleural changes. Consensus was reached between both radiologists in all cases.
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The second chest radiographic pattern noted was patients presenting with normal findings on a chest radiograph and focal air-space disease developing with time (Fig. 2A, 2B). This particular pattern was seen in two (15.4%) of 13 patients. Both of these patients showed increasing air-space disease by their fourth day after admission, with improvement in the air-space disease seen by day 11.
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The third pattern was seen in one patient (1/13, 7.7%) who presented with normal findings on a chest radiograph, but with time developed round pneumonia (Fig. 3). The round pneumonia had worsened by day 4 after admission, with improvement seen on day 17.
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All patients seen in a follow-up clinic 1 week after discharge had normal findings on chest radiographs.
Bilateral disease was seen in seven (53.8%) of 13 patients of our group. Disease limited to the right lung was seen in four (30.8%) of 13 patients, and two (15.4%) of 13 patients had disease only in the left lung. All of our patients (13/13, 100%) showed air-space disease in the mid to lower lung, with almost half (6/13, 46.2%) showing additional involvement of the upper lung.
There was no evidence of pleural change or pleural effusions. No lymphadenopathy was noted. No nodules, cavities, or airway changes were seen in our patients.
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Three distinctive patterns of chest radiographic abnormalities were seen. The most common pattern was focal peripheral air-space disease at presentation with gradual resolution (76.9% of our patients). Some of our patients presented with normal findings on the initial chest radiographs and later developed either focal air-space disease (15.4%) or round pneumonia (7.7%).
Bilateral disease was observed in 53.8% of the patients, and unilateral disease was seen in 46.2% of our patients. All of our patients (13/13, 100%) showed air-space disease in the mid to lower lung, with almost half (46.2%) showing additional upper lung involvement.
SARS is an emerging infectious disease, and a paucity of reports are present in the current literature. In a study of 138 suspected cases of SARS during a hospital outbreak in Hong Kong, Lee et al. [6] reported that the initial chest radiographic findings were similar to other causes of bronchopneumonia but with a predominant involvement of the peripheral zone. Approximately 55% of their patients showed unilateral disease, with the remaining 45% exhibiting multifocal unilateral or bilateral disease.
In another recent study, Wong et al. [12] described the chest radiographic appearance and patterns of progression of 138 patients with SARS. The majority of their patients showed peripheral air-space opacity, with predominance for the lower lung zones and the right lung.
Three studies have described the characteristic of SARS patients in Canada. Müller et al. [13] reviewed the radiographic findings of SARS in four patients from Vancouver, Canada, and eight patients from Hong Kong. They found that the most common radiographic manifestations of SARS were unilateral or bilateral ground-glass opacities or focal unilateral or bilateral areas of consolidation. Poutanen et al. [2] summarized the initial findings of SARS in Canada. They described bilateral lower lung involvement in 75% of their patients. A more recent study by Booth et al. [11] also described the clinical characteristics and short-term outcomes of SARS in 144 patients in Toronto. Most of their patients showed multifocal infiltrates that progressed during hospitalization, although 25% had normal findings on chest radiographs at presentation, 42% of whom never developed an infiltrate. Three percent of their patients developed pneumothoraces while hospitalized.
Tsang et al. [5] described focal or patchy air-space disease as the most common initial presentation of SARS in 10 epidemiologically linked patients in Hong Kong, where they found that 80% of their patients had lower lung involvement, whereas 10% had changes in the upper lungs.
The majority of our patients presented with focal peripheral air-space disease. One of our patients developed a round pneumonia, a pattern that has been described in only a few other studies [6, 13]. None of our patients exhibited an interstitial pattern, in contrast to Poutanen et al. [2] who reported that five of nine patients presented with a subtle reticular interstitial pattern that either resolved or progressed to air-space disease.
We found a predominance of bilateral disease, and our results are more comparable to those presented by Lee et al. [6] than by Poutanen et al. [2], Booth et al. [11], or Wong et al. [12]. Although all of our patients had involvement of the mid to lower lungs, we found a higher percentage of upper lung involvement than has been reported (46.2%). An initial presentation with normal findings on a chest radiograph was also seen by Tsang et al. [5], Booth et al. [11], Wong et al. [12], and Müller et al. [13]. Three of our patients presented with normal findings on a chest radiograph and subsequently developed air-space disease changes, although they were focal in nature. These findings are in contrast to those of Tsang et al., whose patient went on to develop diffuse opacification. Twenty-nine of 30 patients in the Wong et al. study who presented with normal findings on a chest radiograph developed air-space opacities, although the characteristics of the opacities (i.e., focal vs diffuse) were not described by the authors. The patient who presented with normal findings on a chest radiograph in the Müller et al. study showed ground-glass opacification and areas of consolidation on high-resolution CT. None of the chest radiographic findings of the patients in our study remained normal, whereas normal findings on chest radiographs at presentation remained normal in 15 of 36 patients in the Booth et al. study [11].
We found no evidence of pleural thickening, effusion, lymphadenopathy, cavities, or significant airway changes in any of our patients in keeping with the other studies in the literature [2, 5, 6, 12, 13]. However, we found no evidence of pneumothoraces, in contrast to the study by Booth et al. [11] in which 3% of their patients developed pneumothoraces while in the hospital.
Our study is limited by a small sample size of 13 health care workers and only single upright anteroposterior chest radiographs were obtained.
In summary, the chest radiographic manifestations of SARS in a group of health care workers have been described. Most of our patients exhibited focal air-space disease. One of our patients developed a round pneumonia, a pattern that has been described in only a few other studies [6, 13]. We also saw a higher than reported involvement of the upper lungs in our patient population. However, none of these findings are indistinguishable from those seen in other causes of atypical or viral pneumonias. As our understanding of the pathogenesis of SARS increases, so will our understanding of the radiographic manifestations seen in this new infectious disease.
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