key: cord-0264071-4ji543sl authors: Beckwith, P. G.; Karat, A. S.; Govender, I.; Doel, A.; McCreesh, N. S.; Kielmann, K.; Baisley, K.; Grant, A. D.; Yates, T. A. title: Direct estimates of absolute ventilation in primary health care clinics in South Africa date: 2022-03-18 journal: nan DOI: 10.1101/2022.03.17.22272421 sha: 8f5f620d0d841025a5f75b7a382278c193ffb286 doc_id: 264071 cord_uid: 4ji543sl Background Healthcare facilities are important sites for the transmission of pathogens spread via bioaerosols, such as Mycobacterium tuberculosis (Mtb). Natural ventilation can play an important role in reducing this transmission. In primary health care (PHC) clinics in low and middle-income settings, susceptible people, including healthcare workers, are exposed to individuals with infectious pulmonary tuberculosis. We measured rates of natural ventilation in PHC clinics in KwaZulu-Natal and Western Cape provinces, South Africa. Methods and Findings We measured ventilation in clinic spaces using a tracer-gas release method. In spaces where this was not possible, we estimated ventilation using data on indoor and outdoor carbon dioxide levels, under reasonable assumptions about occupants' metabolic rates. Ventilation was measured i) under usual conditions and ii) with all windows and doors fully open. We used these ventilation rates to estimate the risk of Mtb transmission using the Wells-Riley Equation. We obtained ventilation measurements in 33 clinical spaces in 10 clinics: 13 consultation rooms, 16 waiting areas and 4 other clinical spaces. Under usual conditions, the absolute ventilation rate was much higher in waiting rooms (median 1769 m3/hr, range 338-4815 m3/hr) than in consultation rooms (median 197 m3/hr, range 0-1451 m3/hr). Ventilation was better in permanent than in temporary structures. When compared with usual conditions, fully opening existing doors and windows resulted in a median two fold increase in ventilation. Our Wells-Riley estimates show that, following sustained exposure, or contact with highly infectious index cases, some risk of Mtb infection may persist in the best ventilated clinical spaces unless other components of transmission risk are also addressed. Conclusions Among the clinical spaces studied, we observed substantial variation in natural ventilation. Ventilation interventions may have considerable impact on Mtb transmission in this setting. We recommend these form part of a package of infection prevention and control interventions. Introduction 17/02/22 USA; accuracy +/-75 parts per million [ppm] CO2). The concentration of CO2 in the room was then 119 increased by releasing CO2 fire extinguishers for 5-10 seconds. CO2 was mixed with room air using a 120 paddle fan for two minutes, with the aim of achieving a stable and homogeneous CO2 concentration 121 of 3,000-10,000 ppm throughout the space. The fan was then turned off and, after five minutes, any 122 plastic sheeting was removed and the windows and doors were placed in either the usual or ideal 123 configuration. CO2 levels were then recorded every second for a period of approximately five 124 minutes. The aim was to perform three experiments under usual conditions, and three under ideal 125 conditions, yielding six CO2 decay curves under each set of conditions. 126 Rebreathed fraction approach 127 Tracer gas release experiments were not possible in spaces that 1) could not be vacated by patients 128 or clinic staff or 2) were large and very open to the outdoors, meaning high levels of CO2 could not 129 be attained at baseline. Where tracer gas release experiments were not possible, an established 130 approach [23] [24] was adapted to estimate the ventilation rate using data on indoor CO2 131 concentrations, outdoor CO2 concentrations, and occupancy [25] . These experiments were 132 undertaken in eight main waiting areas during working hours when spaces were occupied by 133 patients and staff. 134 In these waiting areas, three CO2 monitors were placed at different central locations and one 135 monitor placed immediately outside the building to capture the CO2 concentration of the 136 replacement air. Measurements were obtained every second. The number of individuals in the room 137 was counted every ten minutes, categorising individuals as aged <1 year, 1-5 years, or >5 years. 138 Data were collected for between one and three hours under each set of conditions (usual and ideal). 139 The tracer gas release experiments produced data similar to those presented in Supplementary 141 Figure 1 . Analysis focussed on the right-hand side of these curves. Specifically, data were included 142 from 30 seconds after the doors and windows were opened until CO2 levels reached 200 ppm above 143 baseline or, where no baseline value was available, until CO2 levels reached 800 ppm. 144 Prior to analysis, the CO2 data were smoothed, using a sixty second moving average (mean), 145 consisting of the 30 seconds before and after each measurement. Using these smoothed data, the 146 natural logarithms of the CO2 concentration measurements were plotted against time in hours. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 17/02/22 6 of air changes per hour, with an associated 95% confidence interval (CI), was obtained using random 151 effects meta-analysis. The absolute ventilation rate (in m 3 /hour) was then calculated as the product 152 of the number of air changes per hour and the room volume. 153 To analyse the paired indoor and outdoor CO2 measurements, we developed an adaptation of the 154 Persily and de Jonge method [24] to allow for non-steady state conditions. The outside CO2 155 concentration was estimated as a mean obtained through curve fitting, using linear interpolation. 156 The indoor CO2 concentration in each space was calculated at each time point by taking the mean 157 value from the three inside monitors. The number of individuals in each age group in the room at 158 each time point was multiplied by their assumed CO2 generation rate to estimate the total CO2 159 generation rate at each time point. Age-specific CO2 production rates were taken from Persily and de 160 Most spaces were only visited on one occasion and, as such, our estimates of ventilation do not fully 169 capture variation in ventilation rates associated with, for example, changes in wind speed or 170 direction. For this reason, when combining data from different spaces, we opted for a descriptive 171 presentation of our results. We avoided calculating pooled effect estimates with associated 172 confidence intervals, as we did not wish to overestimate precision. 173 The Wells-Riley equation models transmission risk for airborne infections as a Poisson process. The 175 approach assumes a well-mixed airspace. It takes into account the time spent in a space, the number 176 of infectious individuals present, the number of 'infectious quanta' they produce per unit time 177 (usually assumed), the volume of air susceptible individuals breathe per unit time, and the absolute 178 ventilation rate [26] . Here, quanta are defined as 'the number of infectious airborne particles 179 required to infect which may be one or more airborne particles ' [26] . is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 Temperature and wind speed 237 We compared temperature and wind speed measured at the nearest weather station at the time we 238 undertook our experiments to the mean temperature and wind speed measured during typical clinic 239 opening hours at the same weather station. 240 Temperatures at the times tracer gas release experiments were conducted were within one and two 241 standard deviations (SDs) of the 3-year mean temperature for 10/12 (83%) and 12/12 (100%) 242 experiment days, respectively, and wind speeds within one and two SDs of the 3-year mean wind 243 speed for 10/12 (83%) and 11/12 (92%) experiment days, respectively ( Figure is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101/2022.03.17.22272421 doi: medRxiv preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022 is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022 The distribution of the number of ACH under both usual and ideal conditions is presented in Figure 302 2B. The same data disaggregated by province, type of room, the age of the building, and whether 303 the community is urban or rural are presented in is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 The distribution of the absolute ventilation rates is presented in Figure 2C . These data, 321 disaggregated by province, type of room, the age of the building, and whether the community is 322 urban or rural, are presented in Figure 5 . Again, we observed substantial variation. The absolute 323 ventilation rate was much higher in waiting rooms ( is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 Supplementary table 3 contains full results for each space in which tracer gas release experiments 330 were performed. Supplementary figure 3 shows the association between wind speed and the 331 absolute ventilation rate for the 26 spaces in which we undertook tracer gas release experiments. 332 is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 Rebreathed fraction experiments 342 The estimated absolute ventilation rates in the eight clinic waiting rooms where the rebreathed 343 fraction approach was used are presented in Figure 6 and supplementary m 3 /hr, respectively) with fully opening existing doors and windows improving the absolute 349 ventilation rate by a median 2.0 fold (range 1.0-6.5). 350 is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022 assumptions about the quanta production rate (Figure 7) . However, ventilation alone cannot eliminate transmission risk in the context of sustained exposure. 372 The is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022 is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 that 'general wards and outpatient spaces' in naturally ventilated buildings should aim for a 417 minimum ventilation rate of 60 litres/second/person (216 m 3 /hr/person) [1] . For 'airborne 418 precaution rooms' (small rooms for accommodating people who may be infectious) the 419 recommended ventilation rate was 160 litres/second/person on average (576 m 3 /hr/person), with a 420 minimum rate of 80 litres/second/person (288 m 3 /hr/person) when wind speed and direction are 421 not favourable. In high burden settings, the transmission risk in general clinic spaces may be 422 equivalent to that in 'airborne precaution rooms', given the high prevalence of undiagnosed TB [31] . We showed that natural ventilation can be improved by two-fold by fully opening available windows 438 and doors. We observed that only 30% of spaces had their windows fully open and all consulting 439 room doors were closed when consultations were taking place. Major barriers to opening existing 440 doors and windows include concerns regards privacy and thermal comfort [32] . In a number of 441 spaces, we observed doors and windows had been closed to allow air conditioning units to function. 442 Detailed qualitative research exploring TB IPC related beliefs and behaviours in the same clinics will 443 be presented separately. 444 An advantage of this work is the wide range of clinical spaces studied. These included: both new and 445 old buildings, temporary and permanent structures, in urban and rural clinics across two provinces. 446 We found that small rooms in temporary structures were particularly badly ventilated. Investment in 447 replacing temporary structures with well-designed permanent structures should be considered, 448 including, where feasible, covered outdoor waiting areas. Low-cost adaptations to existing structures 449 . CC-BY 4.0 International license It is made available under a perpetuity. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 should also be considered. A study of small, poorly-ventilated clinic rooms in Cape Town 450 demonstrated improvements in natural ventilation associated with use of wind driven roof turbines 451 or 'Whirlybird' fans [5] . A study in Lima, Peru measured ventilation before and after making changes 452 to six clinical spaces. These changes ranged in intensity from repairing windows that could not be 453 opened at a cost of USD 25, to building a sheltered outdoor waiting area at a cost of USD 7000. The 454 changes resulted in a median 3.0 fold increase in the ventilation rate [33] . is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 20 variability in ventilation that might be expected with changes in weather and season. However, 483 considering these spaces, we obtained measurements over the course of a calendar year. The days 484 on which we took our measurements were broadly representative with respect to temperature and 485 wind speed. Mathematically, the rebreathed fraction approach should give comparable results, 486 though it required assumptions about occupants' metabolic rate. Direct comparison between the 487 two approaches, in the same space and with the same weather conditions, was not possible, 488 because one method required the space to be occupied and other required it to be empty. It should 489 be noted that while the confidence intervals around the estimates obtained using the rebreathed 490 fraction approach were frequently large, this reflects changes in ventilation rates that occurred over 491 the measurement period -for instance, due to changes in wind speed -as well as the precision of 492 our measurements. 493 Simpler approaches to estimating the absolute ventilation rate are needed. Several have been 494 proposed, such as simply measuring indoor CO2 levels [42] , or estimating transmission risk using the 495 approach described by Rudnick and Milton [23] . However, these approaches do not partition risk 496 into that caused by poor ventilation versus that caused by overcrowding, problems with distinct 497 solutions. A single infectious person may transmit to a single susceptible person in a poorly 498 ventilated space with the low room occupancy only resulting in modest rises in background CO2 499 levels. Furthermore, in our experience, rebreathed fraction measurements may be difficult to 500 interpret where there is rapid flux in levels of occupancy -i.e. in small consultation rooms where 501 patients enter and leave frequently. 502 Ideally, we need approaches to estimate the absolute ventilation rate that do not depend on costly 503 equipment; that can be performed quickly by clinic staff in occupied spaces with minimal training; 504 and with immediate results to guide risk reduction interventions, such as reducing occupancy or 505 opening windows. A possible approach advocated in WHO documents [1][2] makes a set of simple 506 calculations based on wind speed, which must be measured, and the area of the windows of 507 windows and doors. No validation data are presented and the method can only be applied in spaces 508 with openings on opposite walls. One alternative might be a simplified tracer gas release 509 experiment, ideally using an inert substance not usually present in room air. This might mean that 510 small volumes of tracer gas could be released with the room in routine use. We wonder whether 511 concentrations might then be measured using a meter adapted to feed data to a smart phone, with 512 a phone application used to interpret the decay curve. 513 In conclusion, we observed substantial variation in natural ventilation in clinical spaces in primary 514 health care facilities in two provinces of South Africa. The worst ventilated spaces were small rooms 515 . CC-BY 4.0 International license It is made available under a perpetuity. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 where doors and windows had been closed, and temporary structures had lower ventilation rates 516 than permanent structures. Opening all existing doors and windows resulted in meaningful 517 improvements in ventilation. Concerns regarding privacy and thermal comfort may place limits on 518 the ventilation rates that can be achieved. A package of IPC interventions, including those directed 519 at improving natural ventilation, are needed to reduce Mtb transmission in these settings. In future 520 work, we plan to model adaptations to clinic structures that maximise ventilation without 521 compromising thermal comfort. 522 Acknowledgments 523 We are grateful to the clinical and management staff at 10 clinics where we obtained ventilation 524 measurements. We thank Thomas Murray, Harriet Gliddon, and Sinethemba Mabuyakhulu who 525 assisted us with ventilation measurements in KZN. We are grateful to Rod Escombe, Ed Nardell, Jon 526 Taylor, Don Milton and Toby van Reenen for useful discussions about various aspects of ventilation 527 science -they take no responsibility for the content of this manuscript. 528 Author contributions is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022 is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022 is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 Supplementary The configuration of the existing windows and doors in the room observed on the day of room volume measurements (in the case of the tracer gas release experiments); or The configuration of the existing windows and doors found when in use (in the case of the rebreathed fraction approach) Ideal conditions All windows and doors fully opened to allow for maximal ventilation . CC-BY 4.0 International license It is made available under a perpetuity. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 Supplementary is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint The copyright holder for this this version posted March 18, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 Supplementary Figure 3 : The association between wind speed at the nearest weather station and the number of air changes per hour in 26 clinical spaces. 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Indoor 677 Air Modelling the effect 679 of infection prevention and control measures on rate of Mycobacterium tuberculosis 680 transmission to clinic attendees in primary health clinics in South Africa Estimating the 683 contribution of transmission in primary healthcare clinics to community-wide TB disease 684 incidence, and the impact of infection prevention and control interventions MTB/RIF versus sputum microscopy as the initial diagnostic test for tuberculosis: A cluster-688 randomised trial embedded in South African roll-out of Xpert MTB/RIF Shared air: A renewed focus on 691 ventilation for the prevention of tuberculosis transmission WC3 Room J Consulting room 22.1 9 WC6 Room PD Waiting area 54.3 36 WC6 Room TB Waiting KZN1 Room CD Vitals KZN2 Room A Waiting area KZN2 Room C Vitals KZN2 Room HI Consulting 34.6 KZN2 Room V Corridor inside KZN3 Room TB Waiting area KZN6 Room N Consulting room 35 Supplementary Tables Supplementary table 1