Natural infection of guinea pigs exposed to patients with highly drug-resistant tuberculosis.

A natural TB infection model using guinea pigs may provide useful information for investigating differences in transmission efficiency and establishment of active disease by clinical TB strains in a highly susceptible host under controlled environmental conditions. We sought to examine the capacity of naturally transmitted multidrug-resistant Mycobacterium tuberculosis to establish infection and produce active disease in guinea pigs. Guinea pigs were continuously exposed for 4 months to the exhaust air of a 6-bed multidrug-resistant tuberculosis inpatient hospital ward in South Africa. Serial tuberculin skin test reactions were measured to determine infection. All animals were subsequently evaluated for histologic disease progression at necropsy. Although 75% of the 362 exposed guinea pigs had positive skin test reactions [≥6 mm], only 12% had histopathologic evidence of active disease. Reversions (≥6 mm change) in skin test reactivity were seen in 22% of animals, exclusively among those with reactions of 6-13 mm. Only two of 86 guinea pigs with reversion had histological evidence of disease compared to 47% (31/66) of guinea pigs with large, non-reverting reactions. Immunosuppression of half the guinea pigs across all skin test categories did not significantly accelerate disease progression. In guinea pigs that reverted a skin test, a second positive reaction in 27 (33%) of them strongly suggested re-infection due to ongoing exposure. These results show that a large majority of guinea pigs naturally exposed to human-source strains of multidrug-resistant tuberculosis became infected, but that many resolved their infection and a large majority failed to progress to detectable disease.

Inactivating influenza viruses on surfaces using hydrogen peroxide or triethylene glycol at low vapor concentrations.

BACKGROUND: Surfaces in congregate settings, such as vehicles used for mass transportation, can become contaminated with infectious microorganisms and facilitate disease transmission. We disinfected surfaces contaminated with H1N1 influenza viruses using hydrogen peroxide (HP) vapor at concentrations below 100 ppm and triethylene glycol (TEG)-saturated air containing 2 ppm of TEG at 25 degrees C. METHODS: Influenza viruses in aqueous suspensions were deposited on stainless-steel coupons, allowed to dry at ambient conditions, and then exposed for up to 15 minutes to 10 to 90 ppm of HP vapor or TEG-saturated air. Virus assays were done on the solution used to wash the viruses from these coupons and from coupons treated similarly but without exposure to HP or TEG vapor. RESULTS: After 2.5 minutes, exposure to 10-ppm HP vapor resulted in 99% inactivation. For air saturated with TEG at 25 to 29 degrees C, the disinfection rate was about 1.3 log(10) reductions per hour, about 16 times faster than the measured natural inactivation rate under ambient conditions. CONCLUSIONS: Vapor concentrations of 10 ppm HP or 2 ppm TEG can provide effective surface disinfection. At these low concentrations, the potential for damage to even the avionics of an airplane would be expected to be minimal. At a TEG vapor concentration of 2 ppm, there are essentially no health risks to people.

Inactivation of poxviruses by upper-room UVC light in a simulated hospital room environment.

In the event of a smallpox outbreak due to bioterrorism, delays in vaccination programs may lead to significant secondary transmission. In the early phases of such an outbreak, transmission of smallpox will take place especially in locations where infected persons may congregate, such as hospital emergency rooms. Air disinfection using upper-room 254 nm (UVC) light can lower the airborne concentrations of infective viruses in the lower part of the room, and thereby control the spread of airborne infections among room occupants without exposing occupants to a significant amount of UVC. Using vaccinia virus aerosols as a surrogate for smallpox we report on the effectiveness of air disinfection, via upper-room UVC light, under simulated real world conditions including the effects of convection, mechanical mixing, temperature and relative humidity. In decay experiments, upper-room UVC fixtures used with mixing by a conventional ceiling fan produced decreases in airborne virus concentrations that would require additional ventilation of more than 87 air changes per hour. Under steady state conditions the effective air changes per hour associated with upper-room UVC ranged from 18 to 1000. The surprisingly high end of the observed range resulted from the extreme susceptibility of vaccinia virus to UVC at low relative humidity and use of 4 UVC fixtures in a small room with efficient air mixing. Increasing the number of UVC fixtures or mechanical ventilation rates resulted in greater fractional reduction in virus aerosol and UVC effectiveness was higher in winter compared to summer for each scenario tested. These data demonstrate that upper-room UVC has the potential to greatly reduce exposure to susceptible viral aerosols. The greater survival at baseline and greater UVC susceptibility of vaccinia under winter conditions suggest that while risk from an aerosol attack with smallpox would be greatest in winter, protective measures using UVC may also be most efficient at this time. These data may also be relevant to influenza, which also has improved aerosol survival at low RH and somewhat similar sensitivity to UVC.

Characterization of UVC light sensitivity of vaccinia virus.

Interest in airborne smallpox transmission has been renewed because of concerns regarding the potential use of smallpox virus as a biothreat agent. Air disinfection via upper-room 254-nm germicidal UV (UVC) light in public buildings may reduce the impact of primary agent releases, prevent secondary airborne transmission, and be effective prior to the time when public health authorities are aware of a smallpox outbreak. We characterized the susceptibility of vaccinia virus aerosols, as a surrogate for smallpox, to UVC light by using a benchtop, one-pass aerosol chamber. We evaluated virus susceptibility to UVC doses ranging from 0.1 to 3.2 J/m(2), three relative humidity (RH) levels (20%, 60%, and 80%), and suspensions of virus in either water or synthetic respiratory fluid. Dose-response plots show that vaccinia virus susceptibility increased with decreasing RH. These plots also show a significant nonlinear component and a poor fit when using a first-order decay model but show a reasonable fit when we assume that virus susceptibility follows a log-normal distribution. The overall effects of RH (P < 0.0001) and the suspending medium (P = 0.014) were statistically significant. When controlling for the suspending medium, the RH remained a significant factor (P < 0.0001) and the effect of the suspending medium was significant overall (P < 0.0001) after controlling for RH. Virus susceptibility did not appear to be a function of virus particle size. This work provides an essential scientific basis for the design of effective upper-room UVC installations for the prevention of airborne infection transmission of smallpox virus by characterizing the susceptibility of an important orthopoxvirus to UVC exposure.

Fundamental factors affecting upper-room ultraviolet germicidal irradiation - part II. Predicting effectiveness.

Compared with increasing outdoor air ventilation rate, upper-room ultraviolet germicidal irradiation (UVGI) is an attractive technology for lowering the indoor concentration of airborne microorganisms and thereby reducing the risk of airborne transmission of disease. With relatively modest vertical air circulation, most of the air in a room can be irradiated in a relatively brief time period without noise or significant power consumption. The hypothesis tested in this study is that the efficacy of upper-room UVGI to inactivate or kill airborne infectious microorganisms can be determined from an index of UVGI effectiveness, a dimensionless parameter designed to characterize adequacy of vertical air circulation, amount of UVGI provided, and their interaction. This index of effectiveness, which is determined independently of microbiological testing, was found to correlate well with experimental measurements made in a room-size chamber. A comparison of two other dimensionless parameters - the irradiation number and mixing number, from which effectiveness index is calculated - provides insight into whether the quantity of UV provided to the upper room or the intensity of the vertical air circulation is the controlling factor for effective application of upper-room UVGI. The irradiation number is calculated from the UV power output of the fixture(s), a parameter that is fixture specific and much easier to measure than mean fluence rate. An equation was also developed that relates UV fixture power output to mean fluence rate in either the irradiated zone or the entire room. In addition, reductions in viable microorganism concentration due to UVGI predicted from a two-box model are compared with experimental measurements.

Monitoring human exposures to upper-room germicidal ultraviolet irradiation.

After decades of neglect, the resurgence of tuberculosis in the United States between 1985 and 1992 renewed interest in the use of upper room ultraviolet germicidal irradiation to interrupt the transmission of airborne infections. More recently the bioterrorism threat and the appearance of new pathogens with the potential for airborne spread, such as severe acute respiratory syndrome (SARS), have stimulated installations of upper-room irradiation systems. The objective is to flood the entire volume of a room above 6.5 ft with high intensity ultraviolet germicidal irradiation, while minimizing unintentional irradiance below 6.5 ft to avoid eye and skin irritation. Air exchanges between the upper and lower room result in air disinfection of the occupied space. Designers of these systems have adopted the practice of limiting the maximum lower room irradiance at every point to less than the continuous 8-hour time-weighted average threshold limit value, severely limiting the irradiation intensity in the upper room and thereby reducing one of the two major factors determining germicidal effectiveness, the other being room air mixing. The hypothesis of this study is that eye and skin exposure will be well below the recommended safe dose even when maximum eye-level irradiance levels in the room exceed the 8-hour continuous exposure threshold limit. The method employed was to have subjects wear a small photometer that recorded total ultraviolet dose over the period of exposure while subjects went about their normal routine, and comparing this value with a hypothetical dose calculated from the highest measured eye-level irradiance. The results of the study, based on a limited number of observations, confirmed the hypothesis. Observed doses were one-third to a factor of a hundred or more lower than the doses calculated from maximum eye-level irradiances measurements in the occupants' spaces.

Size and UV germicidal irradiation susceptibility of Serratia marcescens when aerosolized from different suspending media.

Experimental systems have been built in laboratories worldwide to investigate the influence of various environmental parameters on the efficacy of UV germicidal irradiation (UVGI) for deactivating airborne microorganisms. It is generally recognized that data from different laboratories might vary significantly due to differences in systems and experimental conditions. In this study we looked at the effect of the composition of the suspending medium on the size and UVGI susceptibility of Serratia marcescens in an experimental system built in our laboratory. S. marcescens was suspended in (i) distilled water, (ii) phosphate buffer, (iii) 10% fetal calf serum, (iv) phosphate-buffered saline (saline, 0.8% sodium chloride), and (v) synthetic saliva (phosphate-buffered saline with 10% fetal calf serum). At low humidity (36%), S. marcescens suspended in water-only medium was the most susceptible to UVGI, followed by those in serum-only medium. The count median diameters (CMDs) for culturable particles from water-only and serum-only media were 0.88 and 0.95 micro m, respectively, with the measurements based on their aerodynamic behavior. The bacteria suspended in phosphate buffer, synthetic saliva, and phosphate-buffered saline had similar UVGI susceptibility and CMD at 1.0, 1.4, and 1.5 micro m, respectively. At high humidity (68%) the CMD of the particles increased by 6 to 16%, and at the same time UVGI susceptibility decreased, with the magnitude of decrease related to the type of suspending medium. In conclusion, the choice of suspending medium influenced both size and UVGI susceptibility of S. marcescens. These data are valuable for making comparisons and deciding on the use of an appropriate medium for various applications.

Report of the Howard Hughes Medical Institute's workshop on the performance of laboratory chemical hoods.

The Howard Hughes Medical Institute sponsored a workshop on laboratory chemical hoods on June 8, 9, and 10, 1998, that brought together 24 experts in the field of laboratory chemical hoods to critically assess the information known about hood performance. Workshop participants developed 31 consensus statements that reflect their collective views on the body of knowledge or lack thereof, for laboratory chemical hoods. The consensus statements fall into four broad categories: (1) hood selection, use, and operation; (2) hood and laboratory design issues; (3) ventilation system design issues; and (4) hood performance testing. The consensus statements include 26 statements on what is known and unknown about the performance of laboratory chemical hoods, 2 statements of definition, and 3 statements that reflect the participants' agreement not to agree. The brief commentary that follows each consensus statement provides guidance and recommendations.

Laboratory chemical hoods: a historical perspective.

A historical review of laboratory fume hoods leads to a consideration of the current status of structural design, operating characteristics (with special reference to face velocity), safety (relative to standardized test results), energy conservation, and certification methods. Noteworthy are (1) the increasing complexity of instrumentation designed to assure full safety function plus airflow modulation to minimize energy consumption; (2) the extreme plasticity of accepted and recommended face velocity values; (3) the insensitivity of standardized hood test protocols to variations in face velocity; and (4) a serious lack of correlation between operator risk, face velocity, and standard hood test results. Safety considerations lead to the selection of laboratory fume hoods having the highest demonstrated containment capability. This is in spite of the fact that most hood operations have a low hazard rating. Energy savings could be realized if the face velocity of each hood could be modulated to match the risk associated with the work being conducted.

The characterization of upper-room ultraviolet germicidal irradiation in inactivating airborne microorganisms.

In this study, we explored the efficacy of upper-room ultraviolet germicidal irradiation (UVGI) in reducing the concentration of Serratia marcescens and Mycobacterium bovis bacille Calmette-Guérin (BCG) aerosols in enclosed places. We constructed a facility (4.5 m x 3 m x 2.9 m) in which both ceiling- and wall-mounted UV fixtures (UV output: 10W and 5W respectively) were installed. The use of ceiling- and wall-mounted UV fixtures (total UV output: 15W) without mixing fan reduced the concentration of S. marcescens aerosols by 46% (range: 22-80%) at 2 air changes per hour (ACH) and 53% (range: 40-68%) at 6 ACH. The use of ceiling- and wall-mounted UV fixtures with mixing fan increased the UV effectiveness in inactivating S. marcescens aerosols to 62% (range: 50-78%) at 2 ACH and to 86% (81-89%) at 6 ACH. For BCG aerosols, UV effectiveness in inactivating BCG aerosols at 6 ACH were 52% (range: 11-69%) by ceiling-mounted UV fixture only (total UV output: 10W) and 64% (51-83%) by both ceiling- and wall-mounted UV fixtures (total UV output: 15W). Our results indicated that the equivalent ventilation rate attributable to upper-room UVGI for BCG aerosols ranged from 1 ACH to 22 ACH for ceiling-mounted UV fixtures and from 6.4 ACH to 28.5 ACH for ceiling- and wall-mounted UV fixtures. Both generalized linear and generalized additive models were fitted to all our data. The regression results indicated that the number of UV fixtures, use of mixing fan, and air exchange rate significantly affected UV effectiveness (p < 0.01, 0.01, 0.01 respectively). However, the strain difference (S. marcescens vs. BCG) appeared less important in UV effectiveness (p = 0.26). Our results also indicated that UV effectiveness increased at higher temperature ((italic)p(/italic) < 0.01), lower dry-bulb temperature ((italic)p(/italic) = 0.21), and colder air from a supply grill located near the ceiling (p = 0.22).

Final report of the consultantship in occupational health provided to the Ministry of Health, Government of Trinidad and Tobago

A two week period was spent in Trinidad becoming familiar with the current status of occupational health and safety programs and programs needs. Activities included interviews with government officials, governmental research institutes, labor and industry representative industrial sites. As there is a total absence of complete reliable statistical information about workplaces and the nature and frequency of occupational injuries and disease, the need for occupaional health services is perceived to be real on the basis of observed industrial practises and by inference from US and British industrial experience. An urgent need is a legal system for acquiring this essential information as a bais for national policy and national priorities with respect to occupational and environmental health matters. Judging from the degraded status of occupational health and safety affairs in the Department of Labor (DOL), it is clearly in the best interests of the working population of T&T to transfer all of DOL's current responsibilities to the Ministry of Health where a comprehensive program of occupational and environmental health protection can be conducted under a single, techically prepared agency. It is strongly recommended that PAHO undertake responsibility for bringing T&T's laws and regulations pertaining to environmental health up-to-date and to do this in the context of preparing model laws for the entire Caribean Comunity. PAHO can perform a second esential function by assisting the Occupational Health Division to complete its recruiting of essential trained personnel. (AU)