A community outbreak of Legionnaires' disease linked to hospital cooling towers: an epidemiological method to calculate dose of exposure.
BACKGROUND: From July to September 1994, 29 cases of community-acquired Legionnaires' disease (LD) were reported in Delaware. The authors conducted an investigation to a) identify the source of the outbreak and risk factors for developing Legionella pneumophila serogroup 1 (Lp-1) pneumonia and b) evaluate the risk associated with the components of cumulative exposure to the source (i.e. distance from the source, frequency of exposure, and duration of exposure). METHODS: A case-control study matched 21 patients to three controls per case by known risk factors for acquiring LD. Controls were selected from patients who attended the same clinic as the respective case-patients. Water samples taken at the hospital, from eight nearby cooling towers, and from four of the patient's homes were cultured for Legionella. Isolates were subtyped using monoclonal antibody (Mab) analysis and arbitrarily primed polymerase chain reaction (AP-PCR). RESULTS: Eleven (52%) of 21 case-patients worked at or visited the hospital compared with 17 (27%) of 63 controls (OR 5.0, 95% CI : 1.1-29). For those who lived, worked, or visited within 4 square miles of the hospital, the risk of illness decreased by 20% for each 0.10 mile from the hospital; it increased by 80% for each visit to the hospital; and it increased by 8% for each hour spent within 0.125 miles of the hospital. Lp-1 was isolated from three patients and both hospital cooling towers. Based on laboratory results no other samples contained Lp-1. The clinical and main-tower isolates all demonstrated Mab pattern 1,2,5,6. AP-PCR matched the main-tower samples with those from two case-patients. CONCLUSION: The results of our investigation suggested that the hospital cooling towers were the source of a community outbreak of LD. Increasing proximity to and frequency of exposure to the towers increased the risk of LD. New guidelines for cooling tower maintenance are needed. Knowing the location of cooling towers could facilitate maintenance inspections and outbreak investigations. (+info
Buildings operations and ETS exposure.
Mechanical systems are used in buildings to provide conditioned air, dissipate thermal loads, dilute contaminants, and maintain pressure differences. The characteristics of these systems and their operations h implications for the exposures of workers to environmental tobacco smoke (ETS) and for the control of these exposures. This review describes the general features of building ventilation systems and the efficacy of ventilation for controlling contaminant concentrations. Ventilation can reduce the concentration of ETS through dilution, but central heating, ventilating, and air conditioning (HVAC) can also move air throughout a building that has been contaminated by ETS. An understanding of HVAC systems is needed to develop models for exposures of workers to ETS. (+info
Germicidal ultraviolet irradiation in air conditioning systems: effect on office worker health and wellbeing: a pilot study.
OBJECTIVES: The indoor environment of modern office buildings represents a new ecosystem that has been created totally by humans. Bacteria and fungi may contaminate this indoor environment, including the ventilation systems themselves, which in turn may result in adverse health effects. The objectives of this study were to test whether installation and operation of germicidal ultraviolet (GUV) lights in central ventilation systems would be feasible, without adverse effects, undetected by building occupants, and effective in eliminating microbial contamination. METHODS: GUV lights were installed in the ventilation systems serving three floors of an office building, and were turned on and off during a total of four alternating 3 week blocks. Workers reported their environmental satisfaction, symptoms, as well as sickness absence, without knowledge of whether GUV lights were on or off. The indoor environment was measured in detail including airborne and surface bacteria and fungi. RESULTS: Airborne bacteria and fungi were not significantly different whether GUV lights were on or off, but were virtually eliminated from the surfaces of the ventilation system after 3 weeks of operation of GUV light. Of the other environmental variables measured, only total airborne particulates were significantly different under the two experimental conditions--higher with GUV lights on than off. Of 113 eligible workers, 104 (87%) participated; their environmental satisfaction ratings were not different whether GUV lights were on or off. Headache, difficulty concentrating, and eye irritation occurred less often with GUV lights on whereas skin rash or irritation was more common. Overall, the average number of work related symptoms reported was 1.1 with GUV lights off compared with 0.9 with GUV lights on. CONCLUSION: Installation and operation of GUV lights in central heating, ventilation and air conditioning systems of office buildings is feasible, cannot be detected by workers, and does not seem to result in any adverse effects. (+info
Follow up investigation of workers in synthetic fibre plants with humidifier disease and work related asthma.
OBJECTIVE: To investigate the clinical and sociomedical outcome in patients with various clinical manifestations of humidifier disease and work related asthma after removal from further exposure. METHODS: Follow up investigation (range 1-13 years) of respiratory symptoms, spirometry, airway responsiveness, sickness absence, and working situation in patients with (I) humidifier fever (n = 12), (II) obstructive type of humidifier lung (n = 8), (III) restrictive type of humidifier lung (n = 4), and (IV) work related asthma (n = 22). All patients were working at departments in synthetic fibre plants with microbiological exposure from contaminated humidification systems or exposure to small particles (< 1 micron) of oil mist. RESULTS: At follow up patients with work related asthma were less often symptom free (37%, 7/19) than patients with humidifier disease (I, II, III) (67%, 16/24). Mean forced expiratory volume in one second (FEV1) of patients with obstructive impairment had been increased significantly at follow up but still remained below the predicted value. Mean forced vital capacity (FVC) of patients with initially restrictive impairment had returned to normal values at follow up. Airway hyperresponsiveness at diagnosis persisted in patients with obstructive impairment (II + IV 14/17, but disappeared in patients with humidifier fever (3/3) and restrictive type of humidifier lung (2/2). In patients with obstructive impairment (II + IV), FVC and FEV1 at diagnosis were negatively associated with the duration between onset of symptoms and diagnosis and the number of years of exposure. Those with positive pre-employment history of respiratory disease had a lower FEV1 at diagnosis. Sickness absence due to respiratory symptoms decreased in all groups of patients after removal from further exposure, but this was most impressive in patients with the humidifier lung (II, III) and patients with work related asthma (IV). At follow up 83% of the patients were still at work at the same production site, whereas 11% received a disability pension because of respiratory disease. CONCLUSION: In patients with work related respiratory disease caused by exposure from contaminated humidification systems or oil mist, removal from further exposure resulted in clinical improvement, although, especially in those with obstructive impairment, signs persisted. Because of the possibility of transferring patients to exposure-free departments most patients could be kept at work. (+info
Airborne infection in a fully air-conditioned hospital. I. Air transfer between rooms.
Measurements have been made of the extent of air exchange between patient rooms in a fully air-conditioned hospital using a tracer-gas method. When the rooms were ventilated at about six air changes per hour, had an excess airflow through the doorway of about 0.1 m.3/sec. and the temperature difference between rooms and corridor was less than 0.5 degrees C., concentrations of the tracer in rooms close to that in which it was being liberated were 1000-fold less than that in the source room. This ratio fell to about 200-fold in the absence of any excess airflow through the doorways. Considerable dilution took place along the corridors so that the concentration fell by around 10-fold for every 10 m. of corridor. (+info
Airborne infection in a fully air-conditioned hospital. II. Transfer of airborne particles between rooms resulting from the movement of air from one room to another.
Experiments were conducted simultaneously with gas and particle tracers to determine the relative loss of particles between source and recipient sites in the hospital ward units. The magnitude of this loss could be accounted for by the assumption of sedimentation from well-mixed air masses during the time required for movement between source and recipients sites. As a consequence of this loss the degree of isolation between patient rooms for airborne particles was between 4 and 25 times greater than that for gaseous contamination, which reflects the actual transport of air between the rooms. The design and construction of portable spinning-disk particle generators suitable for field studies is discussed. (+info
Airborne infection in a fully air-conditioned hospital. II. Transport of gaseous and airborne particulate material along ventilated passageways.
A mathematical model is described for the transport of gaseous or airborne particulate material between rooms along ventilated passageways. Experimental observations in three hospitals lead to a value of about 0.06 m.2/sec. for the effective diffusion constant in air without any systematic directional flow. The 'constant' appears to increase if there is any directional flow along the passage, reaching about 0.12 m. 2/sec. at a flow velocity of 0.04 m./sec. Together with previously published methods the present formulae make it possible to calculate the expected average amounts of gaseous or particulate material that will be transported from room to room in ventilated buildings in which the ventilation and exchange airflows can be calculated. The actual amounts transported in occupied buildings, however, vary greatly from time to time. (+info
Airborne infection in a fully air-conditioned hospital. IV. Airborne dispersal of Staphylococcus aureus and its nasal acquisition by patients.
Studies in a newly built hospital furnished with complete air conditioning where most of the patients are nursed in 6-bed rooms showed that the transfer of air from one patient room to another was very small, especially when there was substantial flow of air in a consistent direction between the patient rooms and the corridor, and that the direct transfer of airborne particles was even less. There was, however, no evidence of any reduction in the rates of nasal acquisition of Staphylococcus aureus compared with those to be found in naturally ventilated hospitals. The numbers of Staph. aureus found in the air of a given room that appeared to have originated from patient carriers in other rooms were many times greater than could be accounted for by direct airborne transfer. Although there was evidence that many carriers were not detected, detailed study showed that this excess transfer to the air of other rooms was genuine. It seems probable on the basis of investigations in this hospital and elsewhere that this excess transfer occurs indirectly, through dispersal from the clothing of the nursing and medical staff into the air of another room of strains with which their outer clothes have become contaminated while dealing with patients. Reduction in direct airborne transfer of micro-organisms from one room to another, whether by ventilation or other means, can only be of clinical advantage if transfer by other routes is, or can be made, less than that by the direct airborne route. (+info