A novel cough aerosol sampling device for sputum-scarce individuals with tuberculosis

Ismail, Ra'eesah

A novel cough aerosol sampling device for sputum-scarce individuals with tuberculosis

Thesis / Dissertation

2025

Publisher

University of Cape Town

Department

Department of Human Biology

Faculty

Faculty of Health Sciences

Abstract

Introduction In 2021, there were 10.6 million tuberculosis cases worldwide, with 1.6 million deaths. Bacterial infection occurs when aerosol droplets enter the respiratory tract and travel to the lungs, causing pulmonary disease. If untreated, the disease has a 50% mortality rate. TB diagnostics require a sputum sample to conduct tests to confirm the presence of Mtb but more than 15% of patients have difficulty producing this sample. A cough aerosol sampling system (CASS) can collect aerosol droplet samples for testing when sputum sampling is not possible. These systems rely on inertial impaction whereby particles are sorted based on their diameter. Thus, CASS also offers information regarding the infectivity of the patient based on their expelled aerosol sizes. This is because smaller respiratory droplets can travel to the smallest structures of the lung and are more likely to cause infection. CASS is a useful technology in field sampling in place of sputum sampling. However current systems are bulky, heavy and not optimised for field testing in resource limited settings – which this project aims to address. Methods & Materials The methodology included designing and developing a physical prototype of a novel miniaturised cough aerosol sampling system (Mini CASS). This device was designed in subsystems, namely the impaction cascade, pump system, mask part and casing. All subsystems followed a rapid prototyping approach characterised by multiple design iterations. The impaction cascade design was guided by Marple and Liu's methodology (1976). This included testing various impaction substrates. Furthermore, it was optimised by computational fluid dynamics. The entire design was evaluated against a set of predefined needs criteria developed through identification of inadequacies in current devices. Verification testing at the Medical Devices Lab (University of Cape Town) included confirmation of the aerosol size fractionation capacity of the cascade impactor. Validation testing was conducted at the Centre for Lung Infection and Immunity (Groote Schuur Hospital) to confirm the ability of Mini CASS to collect culturable bioaerosols (M. smegmatis). Results & Discussion A partially disposable, portable and miniaturised CASS was built with a weight and size of less than 1 kg & 40 cm2 respectively. Results of in-silico and verification testing have confirmed the ability of the device to perform size fractionation with atleast a 30% efficiency per stage. The device successfully collected nebulised M. smegmatis & M. bovis. Culture confirmation of the bacteria proves this as a viable impactor with atleast 3 colony forming units on each stage, comparable to current CASS systems. Conclusion The final Mini CASS prototype exhibited favourable characteristics of being lightweight and easily portable. It fared well in tests conducted to assess viability, proving its capability to collect bioaerosol samples for culture from coughing. It exhibited the ability to fractionate aerosol samples to provide a semi-quantitative measure of infectiousness with known particle sizes and efficiencies. This proof-of-concept device shows CASS technology can be optimised for use in the clinical setting, thereby enabling it to become a more powerful sampling and research tool. The lightweight, easy to use technology has the potential for use at home or temporary sampling sites.

Keywords

Cough

Tuberculosis

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