Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The annual risk of infection (ARI), a measure of recent transmission, has been described as the most
important parameter in tuberculosis (TB) epidemics. Nevertheless, mounting evidence suggests all
factors contributing to TB transmission are not yet completely understood. This research was
performed to investigate the role various parameters, e.g. overcrowding, period of infectivity,
ventilation, and infectivity of source cases, play in TB transmission. An established airborne
transmission risk model, the Wells-Riley equation (WRE), was modified to account for scenarios
where unknown numbers of infectious individuals may be present. Subsequently, the ARI for three
indoor locations conducive to TB transmission were calculated. Two locations (households and
minibus taxis) were identified in a social mixing survey conducted within a South African
community where TB is endemic as a part of this research. The third location (prison) was
identified in an earlier independent study in the same community. The impact various interventions
could have in reducing the ARI associated with each location was explored. Poor ventilation, severe
overcrowding, extended exposure periods, and high incidence rates contributed to high TB
transmission risks in each location. The household-associated ARI was related to the number of
resident adults. Current TB control programs will only reduce the ARI if household ventilation
levels are improved simultaneously. Similar reductions in the ARI could be achieved by trebling
current ventilation levels or by separating child and adult sleeping areas. Neighbouring households
can also contribute substantially to the ARI. The minibus taxi-associated ARI for drivers and
commuters was considerable but readily reduced by opening windows or keeping the fresh-air fan
on. Reducing TB case prevalence through active or passive case-finding would reduce the ARI
substantially. The prison-associated ARI was proportional to levels of overcrowding. No single
intervention, such as improved ventilation, decreased lock-up time, or improved case-finding,
would decrease the ARI substantially, but concurrent implementation of all of them to meet national
or international standards would. This research shows TB is not only transmitted in epidemics by
highly infectious TB cases, but that any TB case, no matter how infectious, has the potential to
infect susceptible people under the right conditions. / AFRIKAANSE OPSOMMING:Die jaarlikse infeksierisiko (ARI) – maatstaf van onlangse siekteoordrag – word as die
belangrikste parameter in tuberkulose- (TB-)epidemies bestempel. Nietemin dui toenemende
bewyse daarop dat nie álle faktore wat tot TB-oordrag bydra, volledig verstaan word nie. Hierdie
navorsing is onderneem om ondersoek in te stel na die rol van verskillende parameters –
byvoorbeeld oorbevolking, tydperk van aansteeklikheid, ventilasie en die aansteeklikheid van
brongevalle – in TB-verspreiding. Gevestigde model vir die raming van siekteverspreiding deur
die lug, die Wells-Riley-vergelyking (WRE), is aangepas vir scenario’s waar onbekende aantal
aansteeklike individue moontlik aanwesig is. Daarna is die ARI bereken vir drie ingeslote ruimtes
wat TB-oordrag bevorder. Twee van die ruimtes (huishoudings en minibustaxi’s) is ten tyde van die
navorsing uitgewys in sosialevermengingsopname in Suid-Afrikaanse gemeenskap waar TB
endemies is. Die derde ruimte (gevangenisse) is uitgewys in vroeëre onafhanklike studie in
dieselfde gemeenskap. Die navorser het gevolglik bepaal watter moontlike impak verskillende
intervensies op die verlaging van die ARI in elke ruimte het. Swak ventilasie, ernstige
oorbevolking, verlengde blootstellingstydperke en hoë voorkomsyfers het in elke ruimte tot hoë
TB-oordragrisiko bygedra. Die huishoudingsverwante ARI het verband gehou met die aantal
volwassenes wat in die huis woon. Huidige TB-beheerprogramme sal slegs die ARI kan verlaag
indien huishoudelike ventilasievlakke terselfdertyd verbeter word. Drie keer beter ventilasievlakke
of die skeiding van kinders en volwassenes se slaapareas kan soortgelyke verlagings in die ARI
teweegbring. Buurhuishoudings kan ook aansienlik tot die ARI bydra. Die minibustaxi-verwante
ARI vir bestuurders en pendelaars was beduidend, maar kan betreklik maklik verlaag word deur
vensters oop te maak of die varslugwaaier aan te hou. Die vermindering van die voorkoms van TBgevalle
deur aktiewe óf passiewe gevalle-opsporing kan die ARI ook beduidend verlaag. Die
gevangenisverwante ARI het met vlakke van oorbevolking verband gehou. Geen enkele intervensie
soos beter ventilasie, korter toesluittye of beter gevalle-opsporing sal die ARI aansienlik verlaag
nie, maar die gelyktydige inwerkingstelling van ál hierdie intervensies in pas met nasionale of
internasionale standaarde kan wél. Hierdie navorsing toon dat TB in epidemies nie net deur hoogs
aansteeklike TB-gevalle oorgedra word nie, maar dat enige TB-geval, ongeag hoe aansteeklik, die
siekte in die regte omstandighede na vatbare mense kan oordra.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20195 |
| Date | 03 1900 |
| Creators | Johnstone-Robertson, Simon Peter |
| Contributors | Welte, Alex, Wood, Robin, Stellenbosch University. Faculty of Science. Dept. of Mathematical Sciences. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 107 p. : ill. |
| Rights | Stellenbosch University |
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