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By Y Nakajima, MD, PhD, and T Mori, MD, PhD
Japanhas experienced a resurgence in tuberculosis during the last several years. Oneof the most relevant factors is the rapidly aging population where thepopulation of those older than 65 years has jumped from 8% in 1975 to 17% in1999. This elderly generation grew up in a time when the tuberculosis epidemicsof Japan were fulminate; therefore, they contracted TB. This generation's TBrate has always been high, and they now represent a greater proportion of thetotal population. This affects the overall TB rate of Japan. An increase inelderly citizens with medical problems leads to a higher TB risk. Growinginfectious 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 situationof 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 femalepopulation; and that for those aged 20-29 years it is as high as 3.3 timesgreater than the general population. Precautionary educational programsreviewing the spread of tuberculosis are often outdated.
Transmission of M. tuberculosis
TB, an airborne infection, is caused by the tubercle bacilli. When a patientwith pulmonary TB coughs or sneezes, numerous droplets with tubercle bacilliinside are spread into the air. Droplets larger than 5-10 in diameterrapidly fall to the floor due to their physical weight, while smaller dropletscan remain in the air. These droplets can remain airborne for extended periodsof time, losing their weight through evaporation, leaving only the nucleus of 1-5in size (i.e., one or several tubercle bacilli). The transmission oftubercle bacilli is mainly achieved through inhaling these droplet nuclei intothe 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 aperson coughs or sneezes. A patient diagnosed or suspected of havingsmear-positive tuberculosis should be instructed to wear a disposable surgicalmask, except when alone in an isolation room. This type of mask is able to catchmost larger droplet particles coming from the mouth, as well as limitingmarginal leakage of larger particles. A cloth mask is far less satisfactorycompared with a surgical mask. If the patient doesn't have a mask, he or she isadvised to cover his/her mouth with tissues or a handkerchief when coughing orsneezing.
Secondly, all infectious patients with smear-positive TB need to be isolatedquickly from non-tuberculosis patients. An isolation room is designed withcertain engineering considerations is the best solution.
Procedures to induce coughing should be avoided for patients with definite orsuspected TB. In 1982, Catanzaro observed a high infectivity rate due tofrequent bronchial therapy with a bronchofiberscope for a smear negative,culture positive tuberculosis patient.3
Finally, and most essentially, early diagnosis of tuberculosis is the mosteffective infection control measure. Staff awareness of this problem ismandatory 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 periodof time in a space lacking ventilation, which means that the risk of inhalingfloating tubercle bacilli does not necessarily correlate with the distance fromthe coughing patient. Therefore, for safety reasons, the air of a TB isolationroom should be assumed to be fully contaminated with tubercle bacilli. To reducecontaminants, the room should be designed so that the infectious droplets can beremoved quickly and cannot be dispersed. It includes such engineering measuresas negative room air pressure, frequent air exchanges, using a high-efficiencyparticulate air (HEPA) filter, and an ultraviolet apparatus light system.
Just one air change with fresh air can remove 63% of the suspended particlesfrom the room air.4 If a ventilation system can perform 10air-changes per hour (ACHs), it takes 14 minutes to remove 90% of airbornecontaminants in a room, and 28 minutes to remove 99%.5 Thus, frequentair turnover is effective for clearing airborne contaminants. However, theincreased air exchanges present some problems to building maintenance. It may betoo breezy and noisy inside the room, and the costs for ventilation itself andfor air heating are other problems. Therefore, a recommended compromise of 8 to12 ACHs is allowed.
The ventilation system of isolation rooms should be independent whereverinfectious droplets can be present, so that the air from these contaminatedareas does not spread. However, the exhaust air should still pass through a HEPAfilter to remove infectious particles. A HEPA filter can catch 99.99% ofparticles larger than 0.3Âµ in diameter in the air. This system has been widelyused in healthcare facilities, especially in isolation rooms, and sometimes itis installed inside exhaust ducts. Of course, this system should be maintainedregularly by an expert to ensure proper functioning.
The ultraviolet (UV) ray at a wavelength of 240 nm (nanometers) killstubercle bacilli effectively, and therefore, its radiation can be useful by manymanufacturers.4 To avoid hazards to eyes and skin, it is recommendedto mount a 15-30 watt UV light near or onto the ceiling, so that the ray isdirected to the top layer of the circulating air in a room. If a UV light worksproperly, it has a capacity comparable to ventilation at 10-20 ACHs.4However, UV radiation can be a possible hazard to humans, it can experience aremarkable loss of its energy under humidity (especially higher than 70%), andthere 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 nucleiin the air relies on two factors. One is the device's filtration ability and theother is the leakage of air from its edges. A device can only be called arespirator if it offers highly effective filtration at a low leakage rate.Generally, an N95 respirator is recommended for protection against inhalation oftubercle bacilli. The N95 respirator has the ability to catch 95% of particles(hence its name) of more than 0.3Âµ in diameter and can limit the marginalleakage at less than 10% when fitted properly. Nicas estimated that theprotective ability of the N95 respirator is 18 times better than the mask.6Needless to say, masks must be worn properly and fit the face snugly to beeffective. Improper use of masks could be dangerous. All users of the N95 maskshould practice a fit test using a special system devised for this purpose.
In ordinary clinical care settings for active TB patients, the risk ofinfection to healthcare workers should be minimal, especially when the N95respirator is used properly under the ventilation at 6 air exhanges.7,8However, in cough-inducing procedures, it may be not enough. Protection shouldbe enhanced accordingly using a higher level respirator and more rigorousengineering systems.
TB infection control for healthcare workers and patients is a basicadministrative responsibility. Facility's administrative program should includethe following aspect:
The infection control program in a Japanese hospital
Fukujuji Hospital, Japan Anti-TB Association, is a typical respiratoryhospital 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 itsinfection control program, including using several engineering systems. Thefollowing are the main features of the program's revision:
Engineering measures and their management
A series of engineering measures have been followed in hospitalconstruction. One isolation ward with 41 beds for tuberculosis has beencompletely renovated with an anteroom at its entrance and a negative pressuresystem working in the ward. The room's air pressure is lower than in thecorridor. The ventilation of the ward uses at 12-26 air exchanges through a HEPAfilter unit.
The outpatient respiratory department was newly equipped with an isolationroom for clinical consultation of patients suspected of TB, with negativepressure ventilation at 22 ACHs. Sputum induction booths were installed in theoutpatient department, as well as in a ward. Two negative pressure rooms wereattached to a newly built chest surgery ward. One operation theater withnegative pressure ventilation was extended from an OR ward, to be used foroperative procedures of MDR-TB patients. Panel-type air-cleaning units with HEPAfilter were installed in the dental clinic and the barbershop in the hospital.
The bacteriological laboratory has been renovated completely for infectioncontrol purposes, attaining a P3 level biohazard-standard at the TB bacteriologysection, and the P2 level at others. In addition, the autopsy room wasrenovated. A high-power air-cleaning unit with a HEPA filter was set in thebronchoscopy laboratory. Patients suspected of having TB are examined in thelast place of the day, and lidocaine nebulization is used for bronchoscopy ofthese patients in place of ordinary spraying.
The triage system has been introduced to the outpatient department onseparating untreated TB patients from general patients. In the in-patient wards,TB patients with smear-positive disease are strictly isolated for 2-3 weekswhile they undergo chemotherapy. Then they are moved to less strict isolationward 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 wellas patients' visitors, are requested to wear a N95 respirator, and TB patientsare requested to wear disposable surgical masks.
Other managerial policy includes:
Patient amenity is another important policy in order to maintain the qualityof the infection control program. In a strict isolation ward, some amenity spotswere arranged such as a small lounge, a smoking space, and a small roof garden.Ordering sale service of daily necessities for the patients also becameavailable.
For a complete list of references, visit www.infectioncontroltoday.com.
Y. Nakajima, MD, PhD, is the vice director of Fukujuji Hospital, JapanAnti-Tuberculosis Association in Tokyo. T. Mori, MD, PhD, is the director of theResearch Institute of Tuberculosis of Japan, Anti-Tuberculosis Association,Tokyo, Japan.
For a complete list of references click here