Study On The Contamination Status Of Legionella In Central Air Conditioning Cooling Tower Water, Transmission And Human Infection

Human inhaiation or aspiration of contaminated aerosols leads to Legionella infection. Cooling towers, hot and cold water supply systems, humidifiers, shower spa and artifical respiration may become pollution. Among them, central conditioning cooling towers have been the most concerned. There are many outbreaks of Legionnaires disease (LD) that eventually traced to cooling tower. We used three sections to investigate the role of central air conditioning system in the propagation of LD: First, the contamination status of Legionella in central air conditioning cooling tower water (infection source); Second, the mode of transmission of legionella in the central air conditioning systems (transmission); Third, the effect of cooling tower legionella pollution on the level of legionella antibody of workers in public place (susceptible).PartⅠStudy on the contamination status of legionella in central air conditioning cooling tower waterObjective To investigate the contamination status of legionella in central air conditioning cooling tower water and its growth factors. Methods We randomly selected 148 places with a central air conditioning system, in which conducted environmental investigation, detected legionella of the cooling tower water and some indicators of the growth of legionella. Results The legionella positive rate of central air conditioning cooling tower water was 75%. LP1 accounted for 65.5%, LP2-8, L.micdadei and L.bozemanii were detected. Total number of colonies and algae were 10-680000 CFU/mL and 6000-107a/l respectively. The difference of legionella detection rate in different concentrations residual chlorine water samples (P<0.001). Within 1 km of most of cooling towers had densely populated squares, such as residential areas, school, recreation. Conclusions In central air conditioning cooling tower water , legionella pollution was serious, bacterial diversity and LP1 as the advantage. Rich bacteria and algae were beneficial to the growth and reproduction of legionella., but the higher concentration of residual chlorine was inhidited on the groeth of leiongella. Within 1 km of most of cooling towers were high population density, human health had potential threat.PartⅡStudy on mode of transmission of legionella in the central air conditioning systemsObjective To explore the mode of transmission of legionella in the central air conditioning systems. Methods Environmental samples collected from four public places of NanJing City were detected by culture and nested-PCR , analyzed by phylogenetic analysis. Results The legionella positive rate of sediment, cooling water, aerosol near cooling tower, dust in duct surface and indoor supply aerosol were 100.0%, 87.5%, 26.2%, 18.8% and 16.7% respectively. Aerosol samples culture positive rate was 7.1%, and PCR positive rate was 60.2%.The nucleotide sequence similarities of legionella in cooling water and aerosol samplers is more than 95%. Conclusion The main pollution source of legionella pneumophila is cooling water. Legionella can transmit to indoor air by central air conditioning. In the air activity legionella was present, and can be collected by Biosampler liquid impactor with yeast extract.PartⅢCooling tower legionella contamination influence on employee's legionella serum antibody levelObjective To learn health practitioners legionella subclinical infection level, and to evaluate the potential effects of contaminated central air conditioning cooling water to the exposed population. Methods Employees were selected from one place where central air conditioning cooling tower water LP1 had been detected positive,the other place had not central air conditioning. Implementation of the questionnaire, physical examination and serum antibody detection of Legionella. Results The legionella serum total antibody positive rate was 60.2%, and anti-LP1-LP14 were detected. And, anti-LP12 and anti-LP4 was the dominant serotype. The anti-LP1 were significant difference (P=0.047). Conclusion Legionella past infection is widespread in employees. The legionella pollution of cooling tower water had some significance on legionella antibody serum conversion, but this effection was much lower than expected. In addition to cooling tower water, other aquatic environment (hot and cold water systems, spa bath, hospital respirators, etc) should be caused our concern, which easily contanminated by Legionella.