【病毒外文文献】2006 Risk-Stratified Seroprevalence of Severe Acute Respiratory Syndrome Coronavirus Among Children in Hong Kong

ARTICLE Risk Stratified Seroprevalence of Severe Acute Respiratory Syndrome Coronavirus Among Children in Hong Kong PamelaP W Lee MBBS a WilfredH S Wong MSc a GabrielM Leung MD b SusanS Chiu MD FAAP a Kwok HungChan PhD c JosephS M Peiris DPhil c Tai HingLam MD b Yu LungLau MD a Departments of a Pediatrics and Adolescent Medicine b Community Medicine and c Microbiology Queen Mary Hospital University of Hong Kong Pokfulam Hong Kong The authors have indicated they have no financial relationships relevant to this article to disclose ABSTRACT BACKGROUND Severe acute respiratory syndrome was relatively mild in children and the incidence was significantly lower when compared with adults Although previous seroepidemiological studies demonstrated that asymptomatic infection was uncommon among health care workers and adult contacts of patients with severe acute respiratory syndrome it is unclear whether this would extend to the pediatric population OBJECTIVE The purpose of this study was to determine the seroprevalence of severe acute respiratory syndrome coronavirus among asymptomatic children living near Amoy Gardens site of largest community outbreak of severe acute respiratory syndrome in Hong Kong compared with a low risk region where no community transmission occurred METHODS The study was conducted from September to October 2003 Target subjects living in the defined high risk and low risk areas were approached through the schools within the respective localities We recruited 353 and 361 children re spectively from the high risk and low risk areas and collected 3 to 5 mL of blood for severe acute respiratory syndrome coronavirus IgG antibody testing by immu nofluorescence antibody assay and confirmation by neutralization test Parents of all of the subjects who joined the study were contacted by telephone and a standardized questionnaire was administered by a research nurse to collect infor mation including sociodemographic data history of severe acute respiratory syn drome coronavirus infection in the subjects and members of the household history of contact with known cases of severe acute respiratory syndrome pres ence of severe acute respiratory syndrome like symptoms since onset of the severe acute respiratory syndrome epidemic travel history of the child and his her relatives within the 15 days before any such symptom onset use of health service as a result of such symptoms and whether there were deaths of relatives as a result of severe acute respiratory syndrome www pediatrics org cgi doi 10 1542 peds 2005 1476 doi 10 1542 peds 2005 1476 KeyWords severe acute respiratory syndrome SARS SARS coronavirus seroprevalence children Abbreviations SARS severe acute respiratory syndrome AMOY Amoy Gardens NTKLOW Upper and Lower Ngau Tau Kok Estates WFE Wah Fu Estate IgG immunoglobulin G IFA immunofluorescence assay CI confidence interval Accepted for publication Nov 28 2005 Address correspondence to Yu Lung Lau MD Department of Pediatrics and Adolescent Medicine Queen Mary Hospital University of Hong Kong Pokfulam Hong Kong E mail lauylung hkucc hku hk PEDIATRICS ISSNNumbers Print 0031 4005 Online 1098 4275 Copyright 2006bythe AmericanAcademyofPediatrics e1156 LEE et al at Rutgers University on April 11 2015pediatrics aappublications orgDownloaded from RESULTS Two 0 57 of 353 asymptomatic children from the high risk area were tested positive for severe acute respiratory syndrome coronavirus antibody compared with 0 of 361 in the low risk region None of the 14 children who lived in the high risk area and had known contacts with severe acute respiratory syndrome patients were seropositive CONCLUSIONS As in adults subclinical severe acute respira tory syndrome coronavirus infection was rare in chil dren in the 2003 epidemic The very low seroprevalence implies little or no population herd immunity to protect against future resurgence of severe acute respiratory syndrome T HE SEVERE ACUTE respiratory syndrome SARS is a newly emerged infectious disease and its etiology is attributed to a novel coronavirus SARS coronavirus 1 Hong Kong was one of the most severely affected areas with a total of 1755 local residents infected and 302 fatalities 2 Children in contrast to adults had less severe disease and pediatric SARS constituted only 6 9 of the total number of SARS cases in Hong Kong The age specific attack rate was 8 9 cases per 100 000 persons H1102118 years of age 3 compared with 30 0 cases per 100 000 adults Similar findings were also observed from a study in Taiwan where only 7 2 of SARS patients were H1134920 years of age 4 Reviews on clinical features investiga tions and prognostic indicators on pediatric SARS in Hong Kong have been published 3 5 7 however there are a lack of data on possible asymptomatic infection in children at the community level Because clinical SARS in children was mild the important question of whether there were more subclinical infections in this age group remains unanswered Our objective was to determine the seroprevalence of SARS coronavirus among asymptomatic children from 3 large housing estates around the Amoy Gardens where a superspreading event occurred giving rise to 330 SARS cases We compared this with a pediatric sample living in a low risk housing estate with no reported SARS case in a different district METHODS StudyDesign A risk stratified seroprevalence study of children under 15 years old living in a high risk area Amoy Gardens AMOY Upper and Lower Ngau Tau Kok Estates NT KLOW and Telford Gardens compared with those liv ing in a low risk area Wah Fu Estate WFE DefinitionofHigh RiskandLow RiskAreas We defined the vicinity of AMOY and NTKLOW as high risk areas because large community outbreaks 330 cases in AMOY of the total 1755 cases over the territory were documented in these 2 housing estates This was confirmed by Lai et al 8 who mapped the Hong Kong SARS outbreak using geographic information sys tem technology revealing an exceptional spatial cluster ing of infection in the Kwun Tong district where a heavy concentration of cases were found in these 2 residential areas Fig 1A This was the largest single community outbreak of SARS in Hong Kong and worldwide Wah Fu Estate WFE a public housing estate located in Southern Hong Kong Island with similar population density as AMOY and NTKLOW was chosen as a com parator because none of its residents were known to be infected with SARS Subjects Target subjects were 6 to 15 year old primary and jun ior secondary school children living in AMOY Ngau Tau Kok Upper and Lower Estates and Telford Gardens a housing estate located 100 m from NTKLOW who were approached through the schools within the locality Let ters explaining the aim of this study were sent to the principals of 9 primary and secondary schools located in the vicinity of AMOY and NTKLOW and 6 schools agreed to join the study We identified 901 subjects from the participating schools and distributed consent forms to the students for their parents to sign We received 372 returns with a response rate of 40 8 Of these 353 children had blood taken for SARS coronavirus serology Fig 2 Target subjects in the low risk area were those who lived in WFE Six schools located near WFE were ap proached and 5 joined the study We identified 2860 targets and distributed consent forms We received 376 13 1 returns and collected serum samples from 361 children Fig 2 The last known case of SARS in Hong Kong was diagnosed on June 22 2003 This survey and blood collections were conducted during September and Octo ber 2003 The study received ethics approval from the institutional review board of the University of Hong Kong and Hospital Authority which complies with the Declaration of Helsinki Written consent was obtained from parents of all of the participating subjects DataCollection A standardized questionnaire collected information in cluding sociodemographic data history of SARS infec tion in the subjects and members of the household history of contact with known cases of SARS presence of SARS like symptoms fever chills cough shortness of breath headache generalized weakness diarrhea and others since March 2003 travel history of the child and his her relatives within the 15 days before any such symptom onset use of health service as a result of such symptoms and whether there were deaths of relatives as a result of SARS Parents of all of the subjects who joined PEDIATRICS Volume 117 Number 6 June 2006 e1157 at Rutgers University on April 11 2015pediatrics aappublications orgDownloaded from the study were contacted by telephone and the above questionnaire was administered by a trained research nurse LaboratoryAnalysis Three to 5 mL of blood were collected for SARS corona virus immunoglobulin G IgG antibody testing All of the serum samples were initially screened by immuno fluorescence assay IFA and positive results were con firmed by virus neutralization test as recommended by the World Health Organization guidelines on laboratory diagnostic criteria for SARS 9 For the IFA microscopic slides coated with SARS coronavirus strain 6109 in fected FRhK4 cells were incubated with 10 H9262L of serum samples at initial dilution of 1 10 for 30 minutes at 37 C The immunofluorescence titer was taken as the highest dilution that showed positive reaction Serum samples positive at this screening dilution were retested by using twofold serial dilutions 10 Previous studies demonstrated that 93 of SARS patients seroconverted by 4 weeks 11 and 100 seroconverted by 35 days after onset of ill ness 12 Also none of the 2400 healthy blood donor sera were seropositive for SARS coronavirus when tested by IFA indicating a specificity of 100 13 The antibody level remained constant up to 7 months after infection 14 Be cause our subjects had serum samples collected 3 to 4 months after the last reported case of SARS in Hong Kong we presumed that all past infection would have been de tectable and none would be missed as a result of antibody decline in our test procedures Virus neutralization was done on IFA positive sera in a biosafety level 3 laboratory The neutralization titer was defined as the highest dilution of serum which gives 50 cytopathic effect on examination at 72 to 96 hours thereafter A titer of H1102210 was considered as pos itive A sensitivity of 100 was reported in convales cent phase serum samples taken a few weeks after the onset of infection in SARS patients 15 FIGURE 1 A Map showing the cumulative SARS occurrences in Hong Kong according to geographical distribution from February to June 2004 Reproduced with permission from Lai PC Wong CM Hedley AJ et al Understanding the spatial clustering of severe acute respiratory syn drome SARS in Hong Kong Environ Health Perspect 2004 112 1550 1556 BandC Mapsshowingthedistri bution of schools recruited into present study from the low risk area WFE B and high risk area AMOY area C S indicates locations of schools from which no sub ject with positive SARS coronavirus IgG was identified circledS locationsofschoolsatwhichthe2subjectswith positive SARS coronavirus IgG were studying P loca tions of the buildings in which the 2 subjects with posi tive SARS coronavirus IgG were living H18540 locations of buildings where SARS cases were reported e1158 LEE et al at Rutgers University on April 11 2015pediatrics aappublications orgDownloaded from StatisticalAnalysis The H9273 2 test with Yates correction was used to compare categorical data and t test was deployed to compare continuous variables Binomial 95 confidence inter vals CIs were generated for the seroprevalence esti mates Fisher s exact test was used to compare seropos itivity rates between the high versus low risk populations A P H11021 05 was considered statistically sig nificant All of the analyses were conducted on SAS 6 12 SAS Institute Cary NC RESULTS Subject characteristics stratified by risk categories are shown in Table 1 and the locations of the studied areas are shown in Fig 1B and C The SARS coronavirus in fection rate in the high risk area was H1102270 per 1000 people whereas that in the low risk area was 0 1 to 0 4 per 1000 people The high risk area and low risk area had similar population density the number of residents below the age of 15 years was 10 340 per km 2 and 9498 per km 2 respectively The gender ratios of subjects in the 2 groups were similar to those of the children living in the respective areas 16 None of the subjects in either group reported a previous history of SARS Two 0 57 of 353 children 95 CI 0 07 2 0 from the high risk area were found to be seropositive for SARS coro navirus antibody Both had been completely asymptom atic of any SARS like illness since March 2003 until the test All 361 children in the low risk area were seroneg ative seroprevalence 0 95 CI 0 1 0 The high risk versus low risk areas seropositivity rates were not statistically different P H11005 24 The first seropositive case was a 13 year old boy liv ing in Telford Gardens His SARS coronavirus IgG titer was 1 160 by IFA and the neutralization antibody titer was 1 80 He lived with his parents elder sister and grandfather none of them had any clinical symptoms suggestive of SARS or had traveled away from Hong Kong since the beginning of the SARS epidemic and their SARS coronavirus IgG titers were allH110211 20 by IFA The second seropositive case was a 13 year old girl living in NTKLOW with her parents and her father s friend Her SARS coronavirus IgG titer was 1 40 by IFA and the neutralization antibody titer was 1 40 None of her rel atives had clinical symptoms suggestive of SARS or trav eled out of Hong Kong and all of their SARS coronavi rus IgG titers were H110211 10 by IFA In the high risk group 11 3 1 children had close family members diagnosed with SARS including 1 death whereas none of the family members of children in the control group had SARS PH11005 002 Three 0 8 other children had a history of contact with persons who FIGURE 2 Flow diagram showing recruitment of subjects in the high and low risk areas PEDIATRICS Volume 117 Number 6 June 2006 e1159 at Rutgers University on April 11 2015pediatrics aappublications orgDownloaded from were diagnosed to have SARS outside the household All 14 of these children who had known SARS contact were seronegative for SARS coronavirus None of the chil dren in the control group had positive contact history More children in the low risk area 20 4 reported having symptoms during the SARS epidemic compared with the high risk group 12 2 P H11005 004 Chills 9 4 and cough 4 7 occurred significantly more commonly in children from the low risk group com pared with the high risk group 4 8 had chills PH11005 03 and 1 1 had cough P H11005 01 Overall reported rates of respiratory symptoms were lower in the high risk group Most who reported symptoms sought medical attention 93 0 in the high risk group and 81 1 in the low risk group P H11005 14 Despite being unwell 23 3 in the high risk group and 48 6 in the low risk group still went to school DISCUSSION Much progress has been made in characterizing the clin icopathological features and epidemiology of SARS in the past 2 years since its emergence A review of the clinical features of SARS in adults and children showed that there were 2 major differences between adult and pediatric SARS 1 the incidence of SARS in children was substantially lower than in adults and 2 SARS was much milder in children and none died under the age of 18 years worldwide 7 The present study is the first com munity based seroepidemiological survey in children The key question concerns whether asymptomatic infec tion with SARS coronavirus represented another end of the disease spectrum in children and if so whether the potential caseload was significant enough to constitute a source for spread in the community setting The fact that pediatric patients affected by SARS had a relatively mild clinical course led some to postulate that children might have only mild symptoms or remain asymptomatic after infected by SARS coronavirus might never present to the health care system and could thus explain the lower incidence of SARS in the pediatric population Our study showed that within a geographic area where superspreading events had oc curred positive serology for SARS coronavirus in healthy asymptomatic children was also very uncom mon 0 57 and was not statistically different when compared with a low risk area Only 2 cases of asymp tomatic infection with SARS coronavirus were docu mented in our study Subclinical SARS as revealed by positive anti SARS coronavirus IgG in asymptomatic in dividuals has been consistently found to be an uncom TABLE 1 CharacteristicsofSubjects Characteristic High Risk Area NH11005353 Low Risk Area NH11005361 P Gender n Male 187 52 9 173 47 9 18 Female 166 47 0 188 52 1 Age meanH11006SD y 10 5H110062 3 10 5H110062 4 97 Housing type n Private housing 132 37 4 128 35 5 65 Public housing 221 62 6 233 64 5 SARS coronavirus IgG antibody n Positive 2 0 5 0 0 24 Any household member infected by SARS n Yes 11 3 1 0 0 002 No 342 96 9 361 100 Any contact with SARS infected persons outside household n Yes 3 0 8 0 0 24 No 350 99 2 361 100 Any relative s died of SARS n Yes 1 0 3 0 0 99 No 352 99 7 361 100 Any following clinical symptoms n Yes 43 12 2 74 20 4 004 Fever 28 7 9 28 7 8 1 Chills 17 4 8 34 9 4 03 Cough 4 1 1 17 4 7 01 Shortness of breath 1 0 3 2 0 6 1 Headache 4 1 1 8 2 2 4 Generalized malaise 5 1 4 5 1 4 1 Diarrhea 3 0 8 5 1 4 75 Any doctor visits because of clinical symptoms Yes 40 43 90 3 60 74 81 1 14 Still went to school despite having above symptoms Yes 10 43 23 3 36 74 48 6 01 e1160 LEE et al at Rutgers University on April 11 2015pediatrics aappublications orgDownloaded from mon entity across different seroepidemiological surveys in both hospital and community settings A recently published systematic review 17 on SARS coronavirus se roprevalence studies showed that the overall seropreva lence in asymptomatic population groups was 0 1 95 CI 0 02 0 018 The seroprevalence in high risk groups such as health care workers and close con tacts of SARS patients was only slightly higher 0 23 95 CI 0 0 37 when compared with the overall seroprevalence The study concluded that seroconver sion was an extremely rare event in individuals who did not develop SARS and SARS coronavirus infection al most certainly led to clinically apparent disease which in the majority of patients was of great severity war ranting hospitalization during the 2003 epidemic In a study on SARS coronavirus seroprevalence in close con tacts of all SARS patients in Hong Kong only 2 0 19 were seropositive and one of them was a 4 year old boy who lived with his parents and grandfather who all had SARS 15 In fact when restricted to close contacts of SARS cases from AMOY the seroprevalence in that study was 1 of 161 0 62 which was virtually identical to our present estimate PH11005 99 Although symptoms of SARS in children were more nonspecific a majority of patients could be reliably identified by vigilant frontline health care professionals according to stringent diagnostic cri teria for case definition 7 The reported incidence of pe diatric SARS from hospital cases very likely represented the true incidence of SARS in Hong Kong children It was unlikely that subclinical SARS with such a low prevalence could have assumed a role in the spread of SARS within the community There are several reasons to explain the low incidence of SARS in children from an epidemiologic point of view The SARS outbreak in Hong Kong first started in the hospital setting involving mostly health care workers and adult patients There was no reported SARS out break in pediatric wards and it has been routine practice in Hong Kong that children are not allowed to visit hospital wards thereby limiting their risk of exposure to SARS during that critical period The transmissibility of SARS in the community setting was low According to a