【病毒外文文献】2004 Emergency Medical Services Utilization during an Outbreak of Severe Acute Respiratory Syndrome (SARS) and the Incid

CLINICAL INVESTIGATIONS Emergency Medical Services Utilization during an Outbreak of Severe Acute Respiratory Syndrome SARS and the Incidence of SARS associated Coronavirus Infection among Emergency Medical Technicians Patrick Chow In Ko MD Wen Jone Chen MD PhD Matthew Huei Ming Ma MD PhD Wen Chu Chiang MD Chan Ping Su MD Chien Hua Huang EMT P Tsung Chien Lu MD Fuh Yuan Shih MD Fang Yue Lin MD PhD Abstract Objectives This was a study to evaluate the utilization of emergency medical services EMS systems during the outbreak of severe acute respiratory syndrome SARS and to assess the incidence of infection among emergency medical technicians EMTs Methods This was a prospec tive observational study conducted in the EMS system of Taipei Taiwan Probable suspect cases of SARS were de fined by World Health Organization criteria SARS related transports were categorized into 1 requests from hospitals for probable suspect cases of SARS 2 quarantined indi viduals and 3 febrile persons City ambulances were organized into teams A B and C for transports of different perceived risks Data on the EMS volume the transport category the final SARS status of patients and the EMT responsible for the transports were collected The EMS projected volume was computed by previous years data and compared with that collected The SARS incidence among EMTs was assessed by investigating probable SARS P SARS and by surveying the seroprevalence of SARS associated coronavirus SARS CoV antibody Results From March 18 to June 19 2003 there were 7 961 EMS transports similar to the volume projected from previous years 7 506 95 CI 6 688 to 8 324 Of these 1 760 22 1 were SARS related When SARS related transports were excluded there was a 12 2 decrease 95 CI 11 4 to 12 9 in EMS activities Requests from hospitals quarantined individuals and febrile citizens accounted for 23 18 and 59 of SARS related transports Among the 397 P SARS cases in the city of 2 65 million people incidence 0 01 95 CI 0 01 to 0 02 138 35 required EMS transports Two EMTs working in team C the team with the lowest risk developed P SARS One of them died soon thereafter The incidence of P SARS was 0 6 95 CI 0 2 to 2 2 or 0 1 95 CI 0 03 to 0 4 per transport SARS CoV serology was available in 74 1 of EMTs who were alive In addition to the surviving P SARS EMT one EMT from team A the team with the highest risk was seropositive Combining P SARS and the seropositive case three EMTs were infected incidence 1 3 95 CI 0 4 to 3 6 No patient transported by the infected EMTs developed SARS The hospitals serving EMS by the infected EMTs had been involved in a clustered outbreak prior to the EMTs infections Conclusions During the outbreak of SARS the overall EMS volume did not change significantly but the non SARS EMS activities decreased Compared with the general population EMS providers are at higher risk of contracting the SARS virus regardless of different perceived levels of risk Standard protections and procedures for infection control should be strictly followed during trans port and within the hospital environment Key words emergency medical services severe acute respiratory syn drome emergency medical technicians utilization incidence ACADEMIC EMERGENCY MEDICINE 2004 11 903 911 Severe acute respiratory syndrome SARS a respira tory illness caused by a novel coronavirus SARS CoV 1 2 was first recognized in February 2003 and became epidemic in Asia 3 The disease has high potential to be transmitted by droplets and close contacts 4 SARS is known to spread extensively among health care workers HCWs in various set tings 5 7 and health care associated transmission of SARS may further result in clustered outbreaks in the communities 8 Studies in Hong Kong and Toronto reported that 62 and 51 of their infected cases From the Department of Emergency Medicine National Taiwan University Hospital College of Medicine National Taiwan Univer sity PC IK W JC MH MM W CC C PS T CL F YS F YL Taipei Taiwan and Medical Director Committee Taipei Fire Department C HH Taipei Taiwan Received January 6 2004 revision received March 8 2004 accepted March 24 2004 Address for correspondence and reprints Matthew Huei Ming Ma MD PhD No 7 Chung Shan S Road Department of Emergency Medicine National Taiwan University Hospital Taipei 100 Taiwan Fax 886 2 23223150 e mail mattma ha mc ntu edu tw Another SARS article appears on page 973 doi 10 1197 j aem 2004 03 016 ACAD EMERG MED d September 2004 Vol 11 No 9 d www aemj org 903 were HCWs respectively and the majority of them were physicians and nurses 59 to 64 SARS infections among other HCWs were also reported although these reports were much less detailed 5 9 During the SARS outbreak emergency medical services EMS systems were used to move febrile patients to medical facilities for further assessments and care 10 and they were also responsible for the transport of the ill or quarantined people who had close contacts with SARS patients It is possible that EMS personnel were exposed to the SARS virus Up to this time SARS infection among paramedics was only briefly reported without any systematic investiga tion 7 The use of EMS for SARS patients transport as well as SARS infection among EMS providers should be evaluated Information of this kind will be helpful in our prevention strategies for future out breaks of SARS The objectives of this study were to evaluate the use of EMS systems during an outbreak of SARS and to assess the incidence of SARS infection among EMS providers and compare it with that of the general population in an Asian metropolitan area with an outbreak of SARS METHODS Study Design This was a prospective observational study in an Asian metropolitan EMS system during the SARS outbreak The institutional review boards of the city EMS committee approved the surveys in the study Study Setting and Population The metropolitan EMS system under study has 2 65 million residents in an area of 272 square kilometers The EMS configura tion is a fire based single tiered basic life support BLS system There are 41 ambulance squads staffed by 322 EMTs each with at least 264 hours of training Currently only one ambulance squad in the city provides advanced life support ALS services Definitions of Probable Suspect SARS Patients Prob able or suspect cases of SARS were diagnosed based on the case definitions recommended by World Health Organization WHO criteria 11 12 A case was excluded if an alternative diagnosis could fully ex plain the patient s illness Suspect SARS S SARS includes the following 1 patients with after November 1 2002 the symptoms of fever greater than 388C and coughing and breathing difficulties as well as one or more of the following exposures within the ten days prior to the onset of the symptoms close contact with a person who is a sus pect or probable case of SARS history of recent travel to a SARS affected area and recent residence in a SARS affected area 2 patients who have died from unknown acute respiratory diseases after November 1 2002 and have had the above mentioned history of exposure within ten days prior to the development of symptoms Probable SARS P SARS An S SARS case with one of the following was defined as P SARS 1 radio graphic evidence of pneumonia or respiratory distress syndrome RDS on chest radiograph 2 one or more laboratory detection screens positive in SARS CoV related tests or 3 autopsy findings consistent with pathology of RDS without an identifiable cause From March to June 2003 a total of 664 P SARS cases were reported in Taiwan 13 Among these P SARS cases 397 patients 60 were from the largest metropolitan city Taipei especially after an outbreak in one of the municipal hospitals in late April 8 In response to the growing epidemic measures were taken by the government to limit transmission of SARS including widespread use of quarantine 14 Beginning March 18 2003 people who had close contact with a SARS patient were quarantined for ten days In addition beginning April 28 travelers arriv ing on airplane flights from SARS affected areas were also quarantined for ten days 14 Study Protocol After the report of the first P SARS case in Taipei the city EMS organized a special system for the transport of SARS cases or patients of high risk Details of the system are described below Categorization of Patient Transports Conventionally the city EMS system does not get involved in inter hospital transports which are carried out by hospital ambulances However during the SARS outbreak EMS was required to be responsible for all SARS related patient transports including interhospital transfers EMS dispatchers screened all EMS calls with a uni fied protocol to acquire information on the occurrence of fever quarantine status and any diagnosis of SARS All patient transports were categorized into 1 requests from the hospitals for interhospital trans ports of P SARS and S SARS cases or other high risk febrile patients or for transporting recovered P SARS and S SARS patients home 2 individuals under quarantine 14 3 febrile patients seeking emergency care defined as those with subjective fever sensation or objective fever 38 08C measured at home or by EMTs on first contact and 4 other afebrile patients Transports of the first three categories of patients were defined as SARS related patient transports Organization of SARS related Patient Transports The use of EMS teams for SARS related patient trans ports evolved with time and events during the SARS outbreak In the early stage of the outbreak the only ALS squad in the city team A was designated as the primary responding unit for all SARS related patient transports After the in hospital outbreak of SARS on 904 Ko et al d EMS DURING SARS OUTBREAK April 22 in the municipal hospital 8 citizens with fever seeking emergency care were asked to call EMS and all EMS providers were required to measure the tympanic temperature of all patients on first contact As the number of SARS related transports escalated seven additional BLS ambulance squads team B were recruited for transporting individuals under quarantine as well as febrile patients in case team A was not immediately available The other 33 ambulance squads in the city were designated as team C and responded to EMS calls from persons without fever or SARS contact histories On occasions when neither team A nor team B was immediately available the dispatch center would send a nearby ambulance squad from team C to respond to the call Whenever possible teams B and C were excluded from the transport of P SARS patients Figure 1 All EMTs of the city EMS ambu lances were required to monitor their health status by measuring their tympanic temperatures once a day and to report any physical symptoms Measures for Personal Protection and Infection Con trol During the outbreak guidelines on protective equipment and procedures for infection control and precautions issued by the Centers for Disease Control and Prevention 15 were adopted by the city EMS All EMTs were required to undergo in service training regarding the guidelines and to follow them for all SARS related patient transports All ambulance squads had the same access to protective equipment and training in infection control procedures Measurements Overall EMS Utilization The number of overall EMS transports during the study period was obtained and compared with the EMS volume from the same community in the previous year when there was no SARS incidence The projected EMS volume in the same period was calculated using linear regression based on data for the previous four years SARS related EMS Transports The nurses in the dispatch center prospectively collected the EMS trans ports of each SARS related patient category and traced the final diagnosis of these patients The final diagno ses of P SARS and S SARS were made by the consen sus of an expert SARS panel from the Taiwan Centers for Disease Control according to the case definitions see above recommended by the WHO 11 12 The con sensus was made by reviewing all relevant clinical epidemiologic radiographic and laboratory data The date the transport category the ambulance team and the EMTs responding to each transport were recorded The date and the number of all P SARS cases reported from the metropolitan area were also collected and compared with the daily amount of overall SARS related transports to evaluate their correlation in the same time frame Figure 1 Schematic representation of EMS responses for severe acute respiratory syndrome SARS related transports during the outbreak ACAD EMERG MED d September 2004 Vol 11 No 9 d www aemj org 905 Survey of SARS Infection among EMTs In this study SARS infections among EMTs were defined as 1 P SARS by WHO criteria confirmed by the consensus of the expert SARS panel from the Taiwan Center for Disease Control 11 12 or 2 a positive serology result of SARS CoV antibody by indirect immunofluorescence assay IFA 16 in asymptomatic individuals P SARS of EMTs EMTs with fever of more than 388C were to report receive a medical checkup and be quarantined or admitted if necessary The number of P SARS and S SARS cases among studied EMTs and diagnosed by the consensus of the expert panel was obtained from the Department of Health SARS patient registry in September 2003 Seroprevalence of SARS CoV Antibody Blood sam ples of EMTs were obtained from July 15 to August 10 2003 for seroprevalence survey IFA on serum was used for detection of SARS CoV antibody 16 As prior infection with SARS CoV virus would have been exceedingly rare a positive serology result is consid ered indicative of acute or recent infection with SARS CoV in a patient with a SARS like illness 17 Previous research reported that nearly 100 of SARS patients had positive antibody response to SARS CoV during the convalescent phase and the SARS specific immu noglobulin G antibody persisted for more than 12 weeks 18 The reported sensitivity and specificity of IFA to the diagnosis of SARS were higher than 90 four weeks after the disease onset 19 These findings indicate that the profiles of antibodies to SARS might be helpful in epidemiologic surveys In our study serum samples were obtained four weeks after re porting the last probable case in the community and 12 weeks after the initial outbreak The time frame is considered to be appropriate for seroprevalence esti mation The incidence of P SARS and seroprevalence for SARS CoV were reported and analyzed by the num ber of studied EMTs and by the number of transports made when appropriate The incidence of P SARS cases in the studied EMTs was also compared with that of the general population in the city Data Analysis Data were entered processed and analyzed using SPSS for Windows Release 10 0 SPSS Inc Chicago IL Data were reported as the number of events or proportion unless otherwise specified 95 confidence interval 95 CI of proportion was computed Comparison was done using a t test or Fisher s exact test where appropriate All tests were two tailed p 0 05 was accepted as statistically significant RESULTS Utilization of EMS From March 18 to June 18 2003 there were a total of 7 961 city EMS transports Among these 1 760 22 1 were SARS related None of the other 6 201 patients transported by EMS turned out to have SARS Compared with the 7 059 EMS transports during the same period in 2002 there was a 12 8 95 CI 12 0 to 13 6 increase in overall EMS volume or a 12 2 95 CI 11 4 to 12 9 de crease in EMS activities when excluding SARS related transports The projected EMS volume based on pre vious years was 7 506 95 CI 6 688 to 8 324 trans ports The overall number of actual EMS transports collected during the outbreak period was not over whelming SARS related EMS Transports The date and the number of P SARS cases reported from the metropol itan area are presented in Figure 2A Most of the P SARS cases were reported between late April and early June Transports of patients from the hospitals of quarantined individuals and of febrile patients seeking emergency care accounted for 406 23 320 18 and 1 034 59 of SARS related transports respectively The date and the number of SARS related EMS transports are illustrated in Figure 2B The requests for SARS related EMS transports were closely associated with hospital associated outbreaks and the epidemic curve of the disease As seen in Figure 2 the daily transport volume started to escalate after the outbreak at the municipal hospital reached the first peak about two weeks after the outbreak and attained a second peak about four weeks after the initial outbreak Team A responded to 54 of all SARS related transports team B and team C re sponded to 22 and 24 of SARS related transports respectively The SARS related EMS transports by transport categories and by transport teams are listed in Table 1 The numbers of cases that were finally diagnosed as P SARS or S SARS in each transport category are also presented in Table 1 Among the 397 P SARS cases reported in the metro politan area 138 35 95 CI 30 to 40 patients requiredEMStransportinthecourseoftheirtreatment When information on the final diagnoses of all trans portedpatientswasavailable wewereabletocompare the perceived versus actual risks of SARS infection among all patient categories Transports of patients from the hospitals posed a much higher threat of exposure to P SARS or S SARS when compared with the other two patient categories Table 1 When trans portingquarantinedindividualsversusfebrilepatients seeking emergency care EMTs were confronted with similar risks of exposure to P SARS 4 4 vs 2 6 p 0 13 or S SARS 2 8 vs 3 2 p 0 85 patients Incidence of SARS Infection among EMS Personnel P SARS and S SARS of EMTs Two EMTs were di agnosed as having P SARS in early May They had 906 Ko et al d EMS DURING SARS OUTBREAK both worked in team C Table 2 One EMT died soon thereafter The other experienced acute respiratory distress syndrome and was supported with mechan ical ventilation for almost one month He survived and was discharged four months later The incidence of P SARS among all 322 EMTs was 0 6 2 322 95 CI 0 2 to 2 2 and the mortality rate was 0 3 1 322 95 CI 0 1 to 1 7 The overall risk of P SARS per SARS related transport was 0 1 2 1 760 95 CI 0 03 to 0 4 One EMT who worked in team B was diagnosed as having S SARS Although team A responded to the majority of trans ports of P SARS cases from the hospitals none of their staff developed P SARS or S SARS For the general population in the metropolitan area theincidenceofP SARSwas0 01 397P SARSamong 2 65 million residents 95 CI 0 01 to 0 02 Seroprevalence of SARS CoV Antibody among EMS Personnel Beside the EMT from team C who died SARS CoV serology was investigated in 238 74 1 of 321 EMTs including all 87 EMTs from teams A and B and 151 64 5 of the 234 EMTs from team C Table 2 Two EMTs tested positive 2 238 incidence 0 8 95 CI 0 2 to 3 0 for SARS CoV antibody in cluding the one from team C who survived P SARS described above and one EMT from team A This additional seropositive EMT from team A did not develop fever greater than 388C during the outbreak period however he did report tympanic temperature up to 37 78C and rhinorrhea for two days in mid May He denied other associated symptoms of diarrhea cough or headache The subclinical seropositive rate of SARS CoV antibody among EMTs i e excluding the ones already diagnosed as having P SARS was 0 4 1 237 95 CI 0 1 to 2 4 Overall SARS Infection Rate When we combined P SARS cases and seropositive cases a total of three EMTs were infected The overall incidence of SARS infection was 1 3 3 239 95 CI 0 4 to 3 6 among the studied EMTs Table 2 shows the number and the incidence of SARS infection among EMTs by EMS teams Figure 2 A The date and the number of probable severe acute respiratory syndrome SARS cases according to World Health Organization WHO criteria reported from the metropolitan city B The date and the number of EMS transports for each patient category ACAD EMERG MED