Conceived and designed the experiments: JP GL BC WS RY. Performed the experiments: JP KC BC RF CC. Analyzed the data: JP GL KC BC VF. Contributed reagents/materials/analysis tools: JP KC. Wrote the paper: JP GL KC TU BC RF CC VF WS RY BC PL PH.
The authors have declared that no competing interests exist.
There are sparse data on whether non-pharmaceutical interventions can reduce the spread of influenza. We implemented a study of the feasibility and efficacy of face masks and hand hygiene to reduce influenza transmission among Hong Kong household members.
We conducted a cluster randomized controlled trial of households (composed of at least 3 members) where an index subject presented with influenza-like-illness of <48 hours duration. After influenza was confirmed in an index case by the QuickVue Influenza A+B rapid test, the household of the index subject was randomized to 1) control or 2) surgical face masks or 3) hand hygiene. Households were visited within 36 hours, and 3, 6 and 9 days later. Nose and throat swabs were collected from index subjects and all household contacts at each home visit and tested by viral culture. The primary outcome measure was laboratory culture confirmed influenza in a household contact; the secondary outcome was clinically diagnosed influenza (by self-reported symptoms). We randomized 198 households and completed follow up home visits in 128; the index cases in 122 of those households had laboratory-confirmed influenza. There were 21 household contacts with laboratory confirmed influenza corresponding to a secondary attack ratio of 6%. Clinical secondary attack ratios varied from 5% to 18% depending on case definitions. The laboratory-based or clinical secondary attack ratios did not significantly differ across the intervention arms. Adherence to interventions was variable.
The secondary attack ratios were lower than anticipated, and lower than reported in other countries, perhaps due to differing patterns of susceptibility, lack of significant antigenic drift in circulating influenza virus strains recently, and/or issues related to the symptomatic recruitment design. Lessons learnt from this pilot have informed changes for the main study in 2008.
ClinicalTrials.gov
HKClinicalTrials.com
The specter of an influenza pandemic continues to threaten, with annual outbreaks of highly-pathogenic H5N1 in birds
We implemented a prospective cluster-randomized trial
The protocol for this trial and supporting CONSORT checklist are available as supporting information; see
From 30 first-contact outpatient clinics in both the private and public sectors across Hong Kong, we enrolled 944 Hong Kong residents aged at least 2 years, reporting at least two symptoms of influenza-like-illness (ILI) (such as fever ≥38°C, cough, sore throat, coryza, headache, malaise, chills, fatigue, etc.), and living in a household with at least two other individuals none of whom had reported ILI symptoms in the preceding 14 days. These index subjects provided nasal and throat swab (NTS) specimens which were combined and tested with the QuickVue Influenza A+B rapid diagnostic test (Quidel Corp, San Diego, CA) and those subjects with a positive result for influenza A or B were randomized and further followed up. For participants enrolled after June 1, 2007, those index subjects with a negative QuickVue result but a fever ≥38°C were also randomized and further followed up. Data on clinical signs and symptoms were collected for all subjects, and an additional NTS was collected for later confirmation of influenza infection by viral culture.
Following randomization a home visit was scheduled (to take place within 36 hours) to implement the intervention, collect baseline demographic data and NTS from all household members aged ≥2 years, and to provide and describe proper use of a free tympanic thermometer and the daily symptom record sheets. During the 9 days following the initial home visit, all household members were asked to keep symptom diaries, and three further home visits were scheduled at 3, 6 and 9 days after the baseline household visit to monitor adherence to interventions and to collect further NTS from all household members aged ≥2 years. At the final (day 9) home visit, the study nurse collected the symptom diaries and evaluated adherence to interventions by interview and by counting the number of surgical masks remaining or weighing the amount of soap and alcohol left in bottles and dispensers.
All subjects aged 18 years and older gave written informed consent. Proxy written consent from parents or legal guardians was obtained for subjects aged 17 years and younger, with additional written assent from those aged 8 to 17 years. The study protocol was approved by the Institutional Review Board of the University of Hong Kong/Hospital Authority Hong Kong West Cluster and was conducted in compliance with the Declaration of Helsinki
Our study compared three interventions. In the control arm, households received education about the importance of a healthy diet and lifestyle, both in terms of illness prevention (for household contacts) and symptom alleviation (for the index). Households in the face mask arm received the control intervention plus education about the potential efficacy of masks in reducing disease spread to household contacts if all parties wear masks, distribution of a box of 50 surgical masks (Tecnol – The Lite One, Kimberly Clark, Roswell, GA) for each household member (or a box of 75 paediatric masks for children aged 3–7 years), and demonstration of proper face-mask wearing and hygienic disposal. Index subjects and all household contacts were taught to wear masks as often as possible at home (except when eating or sleeping) and also when the index was with the household members outside of the household. Households in the hand hygiene group received the control intervention plus education about the potential efficacy of proper hand hygiene in reducing transmission, distribution of an automatic alcohol hand sanitizer (WHO recommended formulation II, liquid content with 75% isopropyl alcohol, Vickmans Labs Ltd., Hong Kong), liquid hand soap (Avalon organics glycerin hand soap, Petaluma, CA), individual small (125 ml) bottles of alcohol hand gel (Gellygen gel with 70% ethyl alcohol, Brymore SA, Italy), and demonstration of proper hand washing and hand antisepsis
The overall objective of the study was to quantify the efficacy of face masks and/or hand hygiene in reducing transmission of influenza to household contacts at the individual level. Specific objectives of this pilot study were to confirm the feasibility of the study design including the practicability of patient recruitment, randomization and follow-up, the appropriateness of the estimated sample size for a subsequent larger trial in terms of characteristics of local circulating influenza viruses and potential effect sizes, the applicability of the interventions and individual adherence with the interventions.
The primary outcome measure was the secondary attack ratio (SAR) at the individual level i.e. the proportion of household contacts of an index case who subsequently became ill with influenza. We evaluated the SAR using a laboratory definition (at least one follow-up NTS positive for influenza by viral culture or PCR) as the primary analysis, and three different clinical definitions of influenza as secondary analyses. The first definition of clinical influenza was fever ≥38°C or at least two of the following symptoms: headache, coryza, sore throat, aches or pains in muscles or joints, cough, or fatigue. The second definition was at least two of the following signs and symptoms: fever ≥37.8°C, cough, headache, sore throat, aches or pains in muscles or joints
We estimated that we would require 51 households (average size 3.8) in the control arm to allow determination of a secondary attack ratio of approximately 24%
Randomization lists were prepared by a biostatistician (B.J.C.). Eligible study participants were randomly allocated to three groups. The first 100 households were randomized in the ratio 2∶1∶1 and subsequent households were randomized in the ratio 8∶1∶1 using a random number generator (R software). The rationale for changing the randomization ratio was to allow us to gather maximum information about the natural characteristics of influenza transmission in households in the absence of control measures, after evaluating the feasibility of each of the interventions in at least 25 households. Interventions were assigned to households by the study manager (R.O.P.F.) based on the randomization sequence. The allocation to specific intervention arms was concealed to recruiting doctors/clinics throughout.
Participants and those administering interventions were not blinded to the interventions, but participants were not informed of the specific nature of the other interventions applied to other participating households.
Nasal swabs were collected by inserting and rotating a sterile swab (Collection swab; EUROTUBO, Madrid, Spain) into the anterior nares. Throat swabs were collected by rubbing a second sterile swab against the tonsillar fossa. Both swabs were snapped off into a tube containing viral transport medium (5% bovine serum albumin in Earle's balanced salt solution with antibiotic). At recruitment, additional nose and throat swabs were collected using sterile foam swabs and then combined and tested by the QuickVue Influenza A+B rapid diagnostic test.
Specimens collected from index subjects at recruitment were stored in a 2–8°C refrigerator (overnight, if required). Specimens collected during home visits were stored in a cool box with at least two icepacks immediately after collection. Before the end of the day of a home visit, study nurses took samples to the nearest collection point for storage in a 2–8°C refrigerator (overnight, if required) or directly to the central testing laboratory. Samples stored at 2–8°C were delivered to the central testing laboratory by courier in cool boxes en route. Samples were eluted and cryopreserved at −70°C immediately after receipt.
All clinical specimens were cultured on Madin-Darby canine kidney cells with exogenous trypsin (2 ug/ml) added. In households which were successfully followed up with home visits, the clinical specimens collected from index subjects at the recruiting clinic and during the first home visit were additionally tested by reverse transcription polymerase chain reaction (RT-PCR) for influenza A and B viruses if both specimens were negative by viral culture. For household contacts who reported symptoms during the follow-up but whose corresponding clinical specimens (collected within +/−2 days of self-reported fever or other respiratory symptoms) were negative by viral culture, those specimens were additionally tested for influenza A and B by RT-PCR. Additional technical details of the laboratory procedures employed in viral culture and RT-PCR testing are given in
To evaluate the SAR and to compare between groups we used exact binomial 95% confidence intervals, and χ2 tests and multivariable logistic regression models adjusting for potential within-household correlation
Nine hundred and forty-four subjects were initially recruited to the study between February 24 and September 14, 2007.
Characteristics of the 198 subjects are shown in
Control | Face mask | Hand hygiene | ||||||||||
Randomized (n = 127) | Followed up (n = 74) | Randomized (n = 35) | Followed up (n = 22) | Randomized (n = 36) | Followed up (n = 32) | |||||||
Age group (%) | ||||||||||||
2–15 years | 48 | (38%) | 33 | (45%) | 12 | (34%) | 9 | (41%) | 13 | (36%) | 12 | (38%) |
16–30 years | 23 | (18%) | 10 | (14%) | 7 | (20%) | 3 | (14%) | 7 | (19%) | 6 | (19%) |
31–50 years | 32 | (25%) | 17 | (23%) | 11 | (31%) | 6 | (27%) | 10 | (28%) | 10 | (31%) |
50+ years | 24 | (19%) | 14 | (19%) | 5 | (14%) | 4 | (18%) | 6 | (17%) | 4 | (12%) |
No. (%) men | 60 | (47%) | 32 | (43%) | 16 | (46%) | 12 | (55%) | 14 | (39%) | 12 | (38%) |
Symptoms (%) | ||||||||||||
Cough | 99 | (78%) | 62 | (84%) | 24 | (69%) | 13 | (59%) | 33 | (92%) | 29 | (91%) |
Runny nose | 98 | (77%) | 61 | (82%) | 28 | (80%) | 16 | (73%) | 28 | (78%) | 26 | (81%) |
Fatigue / tiredness | 96 | (76%) | 56 | (76%) | 26 | (74%) | 16 | (73%) | 29 | (81%) | 25 | (78%) |
Fever (body temperature≥38°C) | 94 | (74%) | 54 | (73%) | 25 | (71%) | 17 | (77%) | 29 | (81%) | 27 | (84%) |
Headache | 80 | (63%) | 40 | (54%) | 29 | (83%) | 18 | (82%) | 22 | (61%) | 19 | (59%) |
Sore throat | 69 | (54%) | 37 | (50%) | 23 | (66%) | 13 | (59%) | 22 | (61%) | 19 | (59%) |
Aches / pains in muscles or joints | 62 | (49%) | 34 | (46%) | 18 | (51%) | 9 | (41%) | 18 | (50%) | 16 | (50%) |
Onset to randomization interval (%) | ||||||||||||
0–24 hours | 86 | (68%) | 48 | (65%) | 21 | (60%) | 14 | (64%) | 25 | (69%) | 22 | (69%) |
24–48 hours | 35 | (28%) | 22 | (30%) | 12 | (34%) | 8 | (36%) | 7 | (19%) | 7 | (22%) |
48+ hours | 5 | (4%) | 4 | (5%) | 1 | (3%) | 0 | (0%) | 3 | (8%) | 3 | (9%) |
Household contacts | (n = 213) | (n = 65) | (n = 92) | |||||||||
Age group (%) | ||||||||||||
0–15 years | – | – | 32 | (15%) | – | – | 11 | (17%) | – | – | 14 | (15%) |
16–30 years | – | – | 43 | (20%) | – | – | 13 | (20%) | – | – | 17 | (18%) |
31–50 years | – | – | 92 | (43%) | – | – | 28 | (43%) | – | – | 35 | (38%) |
50+ years | – | – | 43 | (20%) | – | – | 12 | (18%) | – | – | 25 | (27%) |
No. (%) men | – | – | 83 | (39%) | – | – | 26 | (40%) | – | – | 37 | (40%) |
Influenza vaccination in the previous 12 months | – | – | 29 | (14%) | – | – | 3 | (1%) | – | – | 12 | (6%) |
We implemented the interventions in the remaining 128 households, and 127 (99%) were successfully followed for all four home visits; one household completed three home visits. (
Time intervals a) from symptom onset in the index subject to randomization; b) from randomization to application of the intervention; c) from symptom onset to application of the intervention.
Influenza could not be confirmed by viral culture or RT-PCR in the index subjects in 6 of the 128 households; therefore we only retained 122 households for analysis of crude SARs. Five household contacts had missing data on age, and these were further excluded for the multivariable regression analyses.
The overall laboratory-confirmed SAR was 6.0% (95% confidence interval 3.8%–9.0%) while the clinical SARs were 18%, 11% and 5% according to the three alternative definitions, respectively, with little difference between intervention arms (
Interval between symptom onset and intervention | Secondary attack ratio (95% CI | |||||||
Control | Face mask | Hand hygiene | ||||||
(n = 205) | (n = 61) | (n = 84) | ||||||
Any | Laboratory confirmed influenza | 0.06 | (0.03, 0.10) | 0.07 | (0.02, 0.16) | 0.06 | (0.02, 0.13) | 0.99 |
Clinical influenza definition 1 | 0.18 | (0.13, 0.24) | 0.18 | (0.09, 0.30) | 0.18 | (0.10, 0.28) | 1.00 | |
Clinical influenza definition 2 | 0.11 | (0.07, 0.16) | 0.10 | (0.04, 0.20) | 0.11 | (0.05, 0.19) | 0.97 | |
Clinical influenza definition 3 | 0.04 | (0.02, 0.08) | 0.08 | (0.03, 0.18) | 0.04 | (0.01, 0.10) | 0.52 | |
(n = 110) | (n = 32) | (n = 41) | ||||||
≤36 hours | Laboratory confirmed influenza | 0.06 | (0.03, 0.13) | 0.12 | (0.04, 0.29) | 0.10 | (0.03, 0.23) | 0.69 |
Clinical influenza definition 1 | 0.17 | (0.11, 0.26) | 0.25 | (0.11, 0.43) | 0.17 | (0.07, 0.32) | 0.76 | |
Clinical influenza definition 2 | 0.11 | (0.06, 0.18) | 0.09 | (0.02, 0.25) | 0.10 | (0.03, 0.23) | 0.98 | |
Clinical influenza definition 3 | 0.04 | (0.01, 0.09) | 0.09 | (0.02, 0.25) | 0.05 | (0.01, 0.17) | 0.44 | |
(n = 95) | (n = 29) | (n = 43) | ||||||
>36 hours | Laboratory confirmed influenza | 0.05 | (0.02, 0.12) | 0.00 | (0.00, 0.12) | 0.01 | (0.00, 0.12) | 0.30 |
Clinical influenza definition 1 | 0.19 | (0.12, 0.28) | 0.10 | (0.02, 0.27) | 0.19 | (0.08, 0.33) | 0.71 | |
Clinical influenza definition 2 | 0.12 | (0.06, 0.20) | 0.10 | (0.02, 0.27) | 0.12 | (0.04, 0.25) | 0.99 | |
Clinical influenza definition 3 | 0.05 | (0.02, 0.12) | 0.07 | (0.01, 0.23) | 0.02 | (0.00, 0.12) | 0.79 |
Confidence intervals were calculated by the exact binomial method, not accounting for within-household correlation, and the resulting intervals may therefore slightly underestimate the uncertainty about the SARs.
By Pearson chi-square test adjusted for within-household correlation.
Clinical influenza definition 1 is fever≥38°C or at least 2 of headache, runny nose, sore throat, aches or pains in muscles or joints, cough, or fatigue. Clinical influenza definition 2 is at least 2 of fever≥37.8°C, cough, headache, sore throat, aches or pains in muscles or joints. Clinical influenza definition 3 is the standard CDC classification of fever≥37.8°C plus cough or sore throat.
n | Laboratory-confirmed influenza | Clinical influenza | |||||||
Definition 1 | Definition 2 | Definition 3 | |||||||
OR | 95% CI for OR | OR | 95% CI for OR | OR | 95% CI for OR | OR | 95% CI for OR | ||
Control group | 202 | 1.00 | 1.00 | 1.00 | 1.00 | ||||
Face mask group | 60 | 1.16 | (0.31, 4.34) | 0.88 | (0.34, 2.27) | 0.87 | (0.30, 2.51) | 2.00 | (0.57, 7.02) |
Hand hygiene group | 83 | 1.07 | (0.29, 4.00) | 0.86 | (0.39, 1.91) | 0.88 | (0.36, 2.14) | 0.80 | (0.22, 2.89) |
Child (aged≤15) | 54 | 1.00 | 1.00 | 1.00 | 1.00 | ||||
Adult (aged 16+) | 291 | 1.75 | (0.43, 7.16) | 0.59 | (0.31, 1.15) | 1.40 | (0.56, 3.53) | 1.28 | (0.36, 4.60) |
Female | 211 | 1.00 | 1.00 | 1.00 | 1.00 | ||||
Male | 134 | 1.10 | (0.52, 2.33) | 0.87 | (0.51, 1.47) | 0.76 | (0.39, 1.48) | 0.99 | (0.38, 2.58) |
Not vaccinated | 308 | 1.00 | 1.00 | 1.00 | 1.00 | ||||
Vaccinated in past 1 year | 37 | 0.46 | (0.07, 2.98) | 1.42 | (0.72, 2.79) | 1.30 | (0.55, 3.08) | 0.63 | (0.10, 4.07) |
Child (aged≤15) index | 52 | 1.00 | 1.00 | 1.00 | 1.00 | ||||
Adult (aged 16+) index | 70 | 0.51 | (0.18, 1.43) | 0.83 | (0.42, 1.66) | 0.82 | (0.36, 1.87) | 0.55 | (0.16, 1.84) |
Female index | 68 | 1.00 | 1.00 | 1.00 | 1.00 | ||||
Male index | 54 | 0.80 | (0.30, 2.13) | 0.95 | (0.48, 1.88) | 0.79 | (0.35, 1.80) | 1.44 | (0.43, 4.85) |
Clinical influenza definition 1 is fever≥38°C or at least 2 of headache, runny nose, sore throat, aches or pains in muscles or joints, cough, or fatigue. Clinical influenza definition 2 is at least 2 of fever≥37.8°C, cough, headache, sore throat, aches or pains in muscles or joints. Clinical influenza definition 3 is the standard CDC classification of fever≥37.8°C plus cough or sore throat.
OR = odds ratio.
A total of 24 index subjects were prescribed antivirals: 12 oseltamivir and 12 amantadine. By excluding these 24 households, the overall laboratory and clinical secondary attack ratios increased to 6.4% and 20%, 12% and 5% respectively, while the adjusted odds ratios of the intervention effects were similar (data not shown). Only three laboratory-confirmed secondary cases (4.5%) were observed in the 67 household contacts of the 24 index cases prescribed antivirals.
The 21 laboratory-confirmed secondary cases recorded a variety of clinical symptoms and 4 (19%) secondary cases were asymptomatic; all 4 asymptomatic cases were confirmed by viral culture. Of the three case definitions of clinical influenza, the second definition (based on
In terms of adherence, 45% (21%) of index subjects (household contacts) in the face mask arm reported wearing a mask often or always during the follow-up period, compared to 30% (1%) and 28% (4%) in the control and hand hygiene arms, respectively. The higher reported compliance in index subjects in the face mask group compared to household contacts was validated when at the final home visits the index subjects had used a median of 12 masks (inter-quartile range, IQR: 6, 18) whereas household contacts had only used a median of 6 (IQR: 1, 20); these include the mask worn and then disposed of by each individual as part of the demonstration and teaching during the initial home visit. A total of 63% (41%) of index subjects (household contacts) in the hand hygiene arm reported washing their hands often or always after sneezing, coughing or cleaning their nose compared to 31% (27%) and 63% (47%) in the control and face mask arms. In the hand hygiene group, households used a median of 56 g (IQR: 27 g, 93 g) of alcohol from the automatic sanitizer, and a median of 88 g (IQR: 63 g, 149 g) of liquid hand soap, while regarding the individual bottles of alcohol hand rub index subjects used a median of 7 g (IQR: 2 g, 13 g) and household contacts used a median of 5 g (IQR: 1 g, 12 g).
There were no reported adverse events, including allergic reactions to the intervention measures or other conditions requiring medical attention.
If an influenza pandemic emerges, the likely limited supply of antivirals and vaccines will mean that non-pharmaceutical interventions have a major role to play in mitigating disease spread
Strengths of our study design include the randomized allocation of interventions, the laboratory-based outcome measures, and our demonstrated ability to observe secondary infections with the implied potential to detect reduction in secondary attack ratios. Whereas the present study was not powered to assess the relative efficacy of the interventions, it has proved successful in demonstrating the feasibility of our study design and the local characteristics of influenza transmission. The present findings have facilitated the planning of a subsequent larger study, described in more detail in
Although we found little effect of the interventions in preventing household transmission, our study was underpowered. Nevertheless, our point estimates are close to null, strongly suggesting true equipoise until a definitive randomized trial with sufficient power (i.e. a much larger sample size) rigorously tests the relative efficacy of these interventions. A larger study will also allow us to explore in more detail the transmission dynamics of influenza in households including finer age stratifications and transmission within and between different age groups, which was not possible in the current study.
We observed generally low adherence to interventions. More than one in four household contacts in the face mask group did not wear a surgical mask at all during the follow-up period. Adherence to the face mask intervention was higher in the index subjects, likely due to their intention to reduce the probability of infecting other household members and possibly because of the recent memory of SARS in 2003, during which the majority (76%) of the general public reported that they wore face masks in public, and most engaged in numerous protective practices
While self-reported hand-hygiene practices were similar across the three groups, we note that contamination of this intervention may be lower firstly because the control and face mask group did not receive the education component on proper hand hygiene, secondly because those groups did not receive the alcohol sanitizer and hand rub. Overall, adherence to the hand hygiene intervention in terms of soap and alcohol use appeared low when benchmarked against rates recommended in health care settings. However we note that a previous randomized community study found that 38% of households used more than 57 g of alcohol hand sanitizer during a 2-week period
Overall, the SAR was lower than we had expected. Only 6% of household contacts developed laboratory-confirmed influenza, whereas 5%–18% of contacts developed clinical influenza, depending on case definitions. This is in contrast to previous studies in France
The variability in clinical SARs depending on the choice of case definition has been noted in previous studies
The dropout was higher than anticipated; all subjects were advised of the study requirements and gave informed consent before being recruited into the study (and tested by rapid influenza test without charge), but 35% of randomized subjects/households refused to allow any home visits. These decisions were independent of the allocated intervention, since the interventions were only revealed during the first home visit. Dropout was higher among the group randomized with a negative result on the rapid diagnostic test (after June 1, 2008), perhaps because subjects interpreted their negative result as indicating they did not have influenza thus did not require follow-up. A negative rapid test result does not rule out influenza virus infection
Other limitations of our study design include the potential bias from recruiting symptomatic subjects, resulting in three distinct effects. First, the use of a point-of-care test to detect influenza virus infection, ensuring that the majority of followed-up households will include an index case with laboratory-confirmed influenza (98% in our study), could also preferentially detect those potential recruits with higher viral shedding and subjects with lower levels of viral shedding would be more likely to receive a false negative rapid test results, and not be recruited. However we note that statistical power would be generally increased if index cases were more infectious since we might therefore observe more secondary transmission; the limitation here relates more to generalizability. Secondly, our design results in an unavoidable delay between onset of symptoms in the index subject and the application of the intervention (
In conclusion, there remains a serious deficit in the evidence base of the efficacy of non-pharmaceutical interventions. The US Centers for Disease Control and Prevention have awarded grants to study non pharmaceutical interventions in community settings
Performance of alternative definitions of clinical influenza versus the gold standard of laboratory-confirmed influenza infection in household contacts.
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Study recruitment versus local influenza activity. a) daily recruitment rate (patients per working day); b) Local sentinel surveillance data of influenza-like-illness (number of ILI consultations per 1000 consultations) by the Centre for Health Protection; c) rate of positive influenza isolations among specimens submitted to the WHO reference laboratory of Queen Mary Hospital, Hong Kong.
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Appendix with additional details of laboratory procedures
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Trial protocol
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CONSORT checklist
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We thank all the doctors, nurses and staff of participating centers for facilitating recruitment; Conrad Lam, Winnie Wai, Yolanda Yan and Eileen Yeung for research support; and all field nurses and health care workers for assistance with recruitment and conducting the home visits.