大型車體雨刷及空調系統棘阿米巴原蟲研究

Abstract

過去文獻證實棘阿米巴原蟲可存在於水體環境及車體空調系統中，流行病學研究則發現職業駕駛有較高的退伍軍人病感染風險，其暴露來源可能來自車體雨刷水或空調系統，然目前仍缺乏職業用大型車體暴露調查資訊。由於與棘阿米巴原蟲共生時，退伍軍人菌較能抵抗惡劣環境並增加致病性，本研究欲評估車輛雨刷水及空調系統棘阿米巴原蟲汙染情形以及其與環境物化因子及退伍軍人菌等生物因子之關聯性，並探討雨刷水空調及操作維護和車體資訊是否影響棘阿米巴原蟲檢出及孳生。據此，本研究於大台北都會地區進行採樣，自85輛客貨運車之大型車體採集其空調出風口抹拭樣本及雨刷水桶和其出水口之水樣，並以聚合酶連鎖反應搭配核酸染劑定量樣本中活性棘阿米巴原蟲濃度。此外，亦分析採集樣本中之退伍軍人菌及異營性細菌以及其他多項物化因子，同時設計問卷收集駕駛的用車與維護行為。 研究發現，在85輛大型車體空調系統中，活性棘阿米巴原蟲檢出率為40%，檢出濃度介於0.004–11.5 cells/cm^2。以Multiple logistic regression with stepwise procedure分析空調出風口抹拭樣本活性棘阿米巴原蟲檢出與否之影響因子，顯示原蟲之檢出顯著受總退伍軍人菌及異營性細菌之正向影響(OR= 5.71, 95% CI= 1.74–18.76及OR= 14.29, 95% CI= 4.11–49.73)，且停靠於有遮蔽室內或室外之車輛有較高之原蟲檢出(OR= 0.32, 95% CI= 0.13–0.81)。另以Multiple linear regression with stepwise procedure分析與空調活性棘阿米巴原蟲濃度相關之影響因子，發現清潔或更換空調過濾網之間隔日數越長，活性棘阿米巴原蟲檢出濃度亦越高(β=0.02, P=0.0002)。 至於在大型車體雨刷水系統中，85輛車之雨刷水桶及出水口活性棘阿米巴原蟲檢出率分別為37.7%及36.5%，陽性檢出濃度介於2.91–5.15 log cells/L及2.76–5.07 log cells/L。雖然雨刷水桶及出水口處原蟲檢出率及檢出濃度無顯著差異，然雨刷水出水口/雨刷水桶濃度比值大於1，顯示管線很可能有生物膜引致原蟲繁殖現象。當以Multiple logistic regression with stepwise procedure分析大型車體雨刷水桶內影響活性棘阿米巴原蟲檢出與否之水質因子，發現雨刷水桶內活性棘阿米巴原蟲檢出受導電度及水溫之正向影響(OR= 3.66, 95% CI= 1.10–12.15及OR= 12.24, 95% CI= 1.27–118.24)，且受到pH值之負向影響(OR= 0.33, 95% CI= 0.12–0.93)。而 Multiple logistic regression with stepwise procedure分別分析影響雨刷水桶及出水口活性棘阿米巴原蟲檢出之車體使用維護因子時則發現，行經工業區或廢水處理地區有顯著較高之機率自雨刷水桶及出水口內檢出活性棘阿米巴原蟲(OR= 7.35, 95% CI= 2.12–25.53及OR= 9.60, 95% CI= 1.95–47.25)，每月平均噴灑雨刷水之次數越多，較不易檢出雨刷水出水口活性棘阿米巴原蟲(OR= 0.08, 95%CI = 0.01–0.60)，固定行車路線為台中以南之車輛，其活性棘阿米巴原蟲濃度較行駛於苗栗以北之車輛高(β=25.6,P=0.03)。 本研究為首次針對車體空調與雨刷水系統進行活性棘阿米巴原蟲的定量，亦是首次發現影響空調與雨刷水內活性棘阿米巴原蟲存在之顯著因子。若能從上述高風險之因子進行環境清潔或控制，將可控制活性棘阿米巴原蟲滋生，以降低民眾暴露甚至感染之此原蟲或是其相關寄生性病原細菌的風險，保護職業駕駛人以及民眾的健康。

Previous studies have shown the presence of Acanthamoeba in aquatic environments and automobile air conditioning system. Epidemiology studies have also shown that occupational drivers are in higher risk of Legionnaires' disease. Contaminated sources, such as automobile windscreen wipers or air conditioning systems, could be potential transmission routes of Acanthamoeba and Legionella spp. However, environmental surveillance of Acanthamoeba in occupational large vehicles is unavailable. Since Acanthamoeba have been known to protect Legionella spp. by enhancing virulence against harsh conditions, this study assesses the relationship between viable Acanthamoeba contamination in windscreen wipers and air conditioning systems and physicochemical and biological parameters. Information about windscreen wipers, air conditioning system maintenance, and vehicle characteristics were collected to determine factors influencing viable Acanthamoeba presence and abundance. Thus, water samples from tanks and outlets of windscreen wiper systems and swab samples from air conditioning vents were collected in long-distance buses and garbage trucks in the Taipei metropolitan area. Furthermore, quantitative real time polymerase chain reaction (qPCR) coupled with ethidium monoazide was performed to quantify the concentration of viable Acanthamoeba, and drivers were surveyed on their maintenance behaviors. This study finds that, in the air conditioning system of eighty-five large vehicles, prevalence of viable Acanthamoeba is 40%; concentration range of viable Acanthamoeba is 0.004-11.5 cells/cm^2. In multiple logistic regression with stepwise procedure for factors influencing viable Acanthamoeba presence in swab samples, total L. pneumophila and heterotrophic bacteria show significant positive association with viable Acanthamoeba (OR= 5.71, 95% CI= 1.74–18.76 and OR= 14.29, 95% CI= 4.11–49.73); Vehicle parks at sheltered outdoor or indoor have greater risk of viable Acanthamoeba presence than those who parks at unsheltered places(OR 0.32, 95%CI 0.13–0.81). Further, in multiple linear regression with stepwise procedure, regular interval of cleaning or replacement air conditioning filters is positively associated with viable Acanthamoeba concentration (β=0.02,P=0.0002). In the windscreen wiper system of eighty-five large vehicles, prevalence of viable Acanthamoeba in tanks and outlets is 37.7% and 36.5%; the positive concentration range of viable Acanthamoeba is 2.91–5.15 log cells/L and 2.76–5.07 log cells/L. Although no significant differences were found between tanks and outlets, viable Acanthamoeba concentration in outlet samples was greater than that in tank samples, a fact indicating the possibility of biofilm in wiper pipeline influencing Acanthamoeba proliferation. Multiple logistic regression with stepwise procedure of large vehicle tanks finds that water temperature and conductivity are positively associated with viable Acanthamoeba presence (OR= 3.66, 95%CI= 1.10–12.15 and OR= 12.24, 95%CI= 1.27–118.24), while pH is negatively associated with viable Acanthamoeba presence (OR= 0.33, 95%CI= 0.12–0.93). In multiple logistic regression with stepwise procedure of vehicle maintenance factors influencing viable Acanthamoeba presence in tanks and outlets finds that vehicles that drive through industrial or sewage treatment areas have higher prevalence of viable Acanthamoeba than those that do not(OR= 7.35, 95% CI= 2.12–25.53 and OR= 9.60, 95% CI= 1.95–47.25), vehicles that have higher frequency of wiper spraying is more unlikely to detect viable Acanthamoeba in wiper outlet (OR= 0.08, 95%CI = 0.01–0.60), and vehicles that drives to the south regular have higher concentration of viable Acanthamoeba in tank(β=25.6,P=0.03). This study is the first to quantify viable Acanthamoeba presence in automobile air conditioning and windscreen wiper systems, and is also the first to indicate the key influencing factors of viable Acanthamoeba presence and abundance in large vehicles. Environmental disinfection and control of risk factors are crucial for reducing exposure to potential viable Acanthamoeba or amoeba-resistant pathogens, and in protecting the health of occupational drivers and the public.