Guidelines for safe sputum collection

Introduction

Sputum specimen examination is the main diagnostic procedure for pulmonary Tuberculosis ; however, the medical procedure (patient coughing) that is used for sputum collection increases the potential for transmission of M. Tuberculosis significantly ; therefore, there is need to administer sputum collection safely in healthcare facilities . The CSIR’s Infrastructure Innovation research group has conducted many TB risk assessments in South African public healthcare facilities for over 10 years. A common finding was that engineering controls for sputum collection were not always adequate, maintained or monitored. Sputum was observed to be collected from toilets, consulting rooms and counselling rooms which implies increased risk of TB transmission. This guideline provide guidance on conducting sputum collection safely for suspected or known infectious TB patients. Although there is a three level hierarchy of control measures; administrative controls, engineering controls and personal respiratory protection to prevent transmission of TB, this guideline is limited to engineering control measures for sputum collection.

Engineering control measures for sputum collection

There are two main types of engineering methodologies that can be utilized for sputum collection; local exhaust ventilation devices and sputum collection/induction rooms.

Local exhaust ventilation devices

Local exhaust ventilation devices capture of airborne contaminants at or near the source before they are dispersed into the work space . The basic components of an LEV device are hood, ductwork, air cleaner and fan . Burgess, et al., identifies two major categories of LEV devices; enclosures and exterior. The major difference between these two is that for enclosures, contaminants are released from inside the device whereas for exterior contaminants are released outside the device. A sputum booth is considered as an example of an enclosure LEV device. Illustrations of an enclosure and exterior LEV devices are shown in Figures 1 and 2 respectively. Figure 1 shows a CSIR designed sputum booth. Technical specifications for the booth that can be used for procurement are included in Appendix A.

Mechanical sputum booth

Table 1 gives a comparison between enclosure and exterior LEV devices.

Table 1. Comparison between enclosure and exterior LEV devices

Local Exhaust Ventilation device	Advantages	Disadvantages
Enclosure Contaminants are released from inside the LEV device. Example is a booth as illustrated in Figure 1.	Complete physical separation between patient and staff which ensures negligible exposure to contaminants hence providing the greatest protection when compared to exterior . Conserves energy when compared to the external LEV since it requires least amount of airflow to ensure adequate control . An exhaust airflow is chosen sufficient to create a negative air pressure inside the LEV; this ensures that contaminated air will not escape from the device . Contaminants are quickly captured due to high air change rates. Therefore shorter contaminants clearance times when compared to sputum collection rooms. Devices with HEPA-filtered exhaust can be used in any room. Can be moved to accommodate room function changes.	Cost is higher than external LEV device approximately R125 000. Requires routine maintenance such as changing the HEPA filter and pre-filter. Booths are not as portable as exterior LEV device.
Exterior Contaminants are released from outside the LEV device. Example is illustrated in Figure 2.	Cost is relatively low compared to complete enclosures. Portable, small enough to be used at patient’s bedside.	Exterior LEV devices are susceptible to cross-drafts which may completely disrupt their performance by disrupting the airflow patterns between the point of contaminant release and the exhaust . Since the contaminants are released into the air surrounding an exterior LEV device and then captured, it is possible for a healthcare worker to be in the path between the contaminant source and the device, and be exposed to the contaminants before they are captured . Does not provide complete physical separation between patient and staff. Requires more supervision of patient to ensure proper placement than complete enclosures. Open windows or doors, or people moving in the area can create drafts, which disrupt the capture of airborne particles.

Testing of LEV devices and sputum collection room

Testing and monitoring of the LEV devices and sputum collection rooms is done to ensure correct continued operation of the systems.

Test	Engineering control	Recommended frequency of testing	Test method	Apparatus	Perfomance specification guideline/ standard
Air pressure difference	Sputum induction room, Enclosure LEV	Daily inspection	2.4.1	Electronic micromanometer, mechanical differential pressure gauge (magnehelic gauge)	Greater than -2.5Pa.
Total air flow rate measurement	Sputum induction room, Enclosure LEV	Once every 6 months	2.4.2	Flowhood with flowmeter or a combination of flowhood and anemometer (thermal or vane)	Greater than or equal to 12 ACH for sputum induction room.
Airflow direction and visualisation	Sputum induction room, Enclosure LEV	Daily inspection	2.4.3	Silk thread, Smoke Tubes, nicotine free electronic cigarettes.	Air should flow into the room and into LEV
Installed HEPA filter system leakage	Enclosure LEV	Once every 6 months	2.4.4	Aerosol generator as per ISO 14644:3 section C.6.3 and aerosol photometer	Filter penetration should not exceed 0,05% as per EN1822 standard.

Test Methods

Air pressure difference test

The test is perfomed to verify the capability of the enclosure LEV and sputum induction room to maintain the specified pressure difference with respect to adjacent spaces. The test should be done with all doors closed. Permanent measuring points should be installed.

Total air flow rate measurement

Measurement of total airflow rate is carried out to calculate the clean air volume supplied to the Sputum induction room and Enclosure LEV per unit time, and this value can be used to calculate the air changes per unit time and airborne particle clearance times.

Airflow direction and visualisation

The purpose of airflow direction tests and visualisation is to confirm that the airflow direction conform to the design and performance specification and also to test for stagnant zones of sputum induction room and Enclosure LEV.

Installed HEPA filter system leakage

The test is perfomed to confirm that the HEPA filter is properly installed by verifying the absence of bypass leakage in the installation and that the filter is free of defects (small holes and damages in the filter medium and frame seal). The test is perfomed by introducing a 0.5µm to 0.7µm (as per ISO 14644:3 section B.6.2.2) aerosol upstream and scanning downstream of the filter.