Stopping the Spread of TB
A Japanese Hospital Case Study
By Y Nakajima, MD, PhD, and T Mori, MD, PhD
Japan has experienced a resurgence in tuberculosis during the last several years. One of the most relevant factors is the rapidly aging population where the population of those older than 65 years has jumped from 8% in 1975 to 17% in 1999. This elderly generation grew up in a time when the tuberculosis epidemics of Japan were fulminate; therefore, they contracted TB. This generation's TB rate has always been high, and they now represent a greater proportion of the total population. This affects the overall TB rate of Japan. An increase in elderly citizens with medical problems leads to a higher TB risk. Growing infectious cases among aged people directly impacts the younger generations, resulting in the recent upsurge of TB rate in these age groups as well.
The rise of TB case rates in nursing symbolizes the epidemiological situation of TB in Japan presently. TB surveillance data indicate that the female nurses' notification rate of all forms of TB of is 2.5 times that of the general female population; and that for those aged 20-29 years it is as high as 3.3 times greater than the general population. Precautionary educational programs reviewing the spread of tuberculosis are often outdated.
Transmission of M. tuberculosis
TB, an airborne infection, is caused by the tubercle bacilli. When a patient with pulmonary TB coughs or sneezes, numerous droplets with tubercle bacilli inside are spread into the air. Droplets larger than 5-10 in diameter rapidly fall to the floor due to their physical weight, while smaller droplets can remain in the air. These droplets can remain airborne for extended periods of time, losing their weight through evaporation, leaving only the nucleus of 1-5 in size (i.e., one or several tubercle bacilli). The transmission of tubercle bacilli is mainly achieved through inhaling these droplet nuclei into the airways.
Blocking transmission of infection in hospitals
Suppress the spread of infectious droplets into the air.
Aerosolized droplets are normally expelled from the mouth or the nose when a person coughs or sneezes. A patient diagnosed or suspected of having smear-positive tuberculosis should be instructed to wear a disposable surgical mask, except when alone in an isolation room. This type of mask is able to catch most larger droplet particles coming from the mouth, as well as limiting marginal leakage of larger particles. A cloth mask is far less satisfactory compared with a surgical mask. If the patient doesn't have a mask, he or she is advised to cover his/her mouth with tissues or a handkerchief when coughing or sneezing.
Secondly, all infectious patients with smear-positive TB need to be isolated quickly from non-tuberculosis patients. An isolation room is designed with certain engineering considerations is the best solution.
Procedures to induce coughing should be avoided for patients with definite or suspected TB. In 1982, Catanzaro observed a high infectivity rate due to frequent bronchial therapy with a bronchofiberscope for a smear negative, culture positive tuberculosis patient.3
Finally, and most essentially, early diagnosis of tuberculosis is the most effective infection control measure. Staff awareness of this problem is mandatory education for infection control professional.
Remove droplet nuclei (tubercle bacilli) from the air.
The airborne particles can be spread throughout a room within a short period of time in a space lacking ventilation, which means that the risk of inhaling floating tubercle bacilli does not necessarily correlate with the distance from the coughing patient. Therefore, for safety reasons, the air of a TB isolation room should be assumed to be fully contaminated with tubercle bacilli. To reduce contaminants, the room should be designed so that the infectious droplets can be removed quickly and cannot be dispersed. It includes such engineering measures as negative room air pressure, frequent air exchanges, using a high-efficiency particulate air (HEPA) filter, and an ultraviolet apparatus light system.
Just one air change with fresh air can remove 63% of the suspended particles from the room air.4 If a ventilation system can perform 10 air-changes per hour (ACHs), it takes 14 minutes to remove 90% of airborne contaminants in a room, and 28 minutes to remove 99%.5 Thus, frequent air turnover is effective for clearing airborne contaminants. However, the increased air exchanges present some problems to building maintenance. It may be too breezy and noisy inside the room, and the costs for ventilation itself and for air heating are other problems. Therefore, a recommended compromise of 8 to 12 ACHs is allowed.
The ventilation system of isolation rooms should be independent wherever infectious droplets can be present, so that the air from these contaminated areas does not spread. However, the exhaust air should still pass through a HEPA filter to remove infectious particles. A HEPA filter can catch 99.99% of particles larger than 0.3µ in diameter in the air. This system has been widely used in healthcare facilities, especially in isolation rooms, and sometimes it is installed inside exhaust ducts. Of course, this system should be maintained regularly by an expert to ensure proper functioning.
The ultraviolet (UV) ray at a wavelength of 240 nm (nanometers) kills tubercle bacilli effectively, and therefore, its radiation can be useful by many manufacturers.4 To avoid hazards to eyes and skin, it is recommended to mount a 15-30 watt UV light near or onto the ceiling, so that the ray is directed to the top layer of the circulating air in a room. If a UV light works properly, it has a capacity comparable to ventilation at 10-20 ACHs.4 However, UV radiation can be a possible hazard to humans, it can experience a remarkable loss of its energy under humidity (especially higher than 70%), and there is the necessity for frequent maintenance of the apparatus.
Personal protection equipment(PPE) offers protection.
Using a mask or a respirator as protection against inspiring droplet nuclei in the air relies on two factors. One is the device's filtration ability and the other is the leakage of air from its edges. A device can only be called a respirator if it offers highly effective filtration at a low leakage rate. Generally, an N95 respirator is recommended for protection against inhalation of tubercle bacilli. The N95 respirator has the ability to catch 95% of particles (hence its name) of more than 0.3µ in diameter and can limit the marginal leakage at less than 10% when fitted properly. Nicas estimated that the protective ability of the N95 respirator is 18 times better than the mask.6 Needless to say, masks must be worn properly and fit the face snugly to be effective. Improper use of masks could be dangerous. All users of the N95 mask should practice a fit test using a special system devised for this purpose.
In ordinary clinical care settings for active TB patients, the risk of infection to healthcare workers should be minimal, especially when the N95 respirator is used properly under the ventilation at 6 air exhanges.7,8 However, in cough-inducing procedures, it may be not enough. Protection should be enhanced accordingly using a higher level respirator and more rigorous engineering systems.
TB infection control for healthcare workers and patients is a basic administrative responsibility. Facility's administrative program should include the following aspect:
- Set up an infection control committee with the guidance of a TB specialist.
- Perform risk assessment for TB infection based on the number and the characteristics of TB patients identified in the facility.
- Develop the infection control guidelines appropriate to your own facility.
- Introduce a patient triage system into the outpatient department.
- Train staff--including doctors--in the prevention and management of tuberculosis.
The infection control program in a Japanese hospital
Fukujuji Hospital, Japan Anti-TB Association, is a typical respiratory hospital in Japan with 91 beds for TB patients in addition to 290 general beds. During the last three years, the hospital has made efforts to revise its infection control program, including using several engineering systems. The following are the main features of the program's revision:
Engineering measures and their management
A series of engineering measures have been followed in hospital construction. One isolation ward with 41 beds for tuberculosis has been completely renovated with an anteroom at its entrance and a negative pressure system working in the ward. The room's air pressure is lower than in the corridor. The ventilation of the ward uses at 12-26 air exchanges through a HEPA filter unit.
The outpatient respiratory department was newly equipped with an isolation room for clinical consultation of patients suspected of TB, with negative pressure ventilation at 22 ACHs. Sputum induction booths were installed in the outpatient department, as well as in a ward. Two negative pressure rooms were attached to a newly built chest surgery ward. One operation theater with negative pressure ventilation was extended from an OR ward, to be used for operative procedures of MDR-TB patients. Panel-type air-cleaning units with HEPA filter were installed in the dental clinic and the barbershop in the hospital.
The bacteriological laboratory has been renovated completely for infection control purposes, attaining a P3 level biohazard-standard at the TB bacteriology section, and the P2 level at others. In addition, the autopsy room was renovated. A high-power air-cleaning unit with a HEPA filter was set in the bronchoscopy laboratory. Patients suspected of having TB are examined in the last place of the day, and lidocaine nebulization is used for bronchoscopy of these patients in place of ordinary spraying.
The triage system has been introduced to the outpatient department on separating untreated TB patients from general patients. In the in-patient wards, TB patients with smear-positive disease are strictly isolated for 2-3 weeks while they undergo chemotherapy. Then they are moved to less strict isolation ward to stay another 2-3 weeks. MDR-TB patients are also under strict isolation. No isolation is used for non-infectious TB patients. Healthcare workers, as well as patients' visitors, are requested to wear a N95 respirator, and TB patients are requested to wear disposable surgical masks.
Other managerial policy includes:
- Set up of the infection control committee
- Regular joint meeting for clinical management of MDR-TB cases
- The surveillance of staff's healthcare
- Committee for staff's training.
Patient amenity is another important policy in order to maintain the quality of the infection control program. In a strict isolation ward, some amenity spots were arranged such as a small lounge, a smoking space, and a small roof garden. Ordering sale service of daily necessities for the patients also became available.
For a complete list of references, visit www.infectioncontroltoday.com.
Y. Nakajima, MD, PhD, is the vice director of Fukujuji Hospital, Japan Anti-Tuberculosis Association in Tokyo. T. Mori, MD, PhD, is the director of the Research Institute of Tuberculosis of Japan, Anti-Tuberculosis Association, Tokyo, Japan.
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