O'Mahony M C, Stanwell-Smith R E, Tillett H E, Harper D, Hutchison J G, Farrell I D, Hutchinson D N, Lee J V, Dennis P J, Duggal H V
Public Health Laboratory Service Communicable Disease Surveillance Centre, London.
Epidemiol Infect. 1990 Jun;104(3):361-80. doi: 10.1017/s0950268800047385.
A large outbreak of Legionnaires' disease was associated with Stafford District General Hospital. A total of 68 confirmed cases was treated in hospital and 22 of these patients died. A further 35 patients, 14 of whom were treated at home, were suspected cases of Legionnaires' disease. All these patients had visited the hospital during April 1985. Epidemiological investigations demonstrated that there had been a high risk of acquiring the disease in the out patient department (OPD), but no risk in other parts of the hospital. The epidemic strain of Legionella pneumophila, serogroup 1, subgroup Pontiac 1a was isolated from the cooling water system of one of the air conditioning plants. This plant served several departments of the hospital including the OPD. The water in the cooling tower and a chiller unit which cooled the air entering the OPD were contaminated with legionellae. Bacteriological and engineering investigations showed how the chiller unit could have been contaminated and how an aerosol containing legionellae could have been generated in the U-trap below the chiller unit. These results, together with the epidemiological evidence, suggest that the chiller unit was most likely to have been the major source of the outbreak. Nearly one third of hospital staff had legionella antibodies. These staff were likely to have worked in areas of the hospital ventilated by the contaminated air conditioning plant, but not necessarily the OPD. There was evidence that a small proportion of these staff had a mild legionellosis and that these 'influenza-like' illnesses had been spread over a 5-month period. A possible explanation of this finding is that small amounts of aerosol from cooling tower sources could have entered the air-intake and been distributed throughout the areas of the hospital served by this ventilation system. Legionellae, subsequently found to be of the epidemic strain, had been found in the cooling tower pond in November 1984 and thus it is possible that staff were exposed to low doses of contaminated aerosol over several months. Control measures are described, but it was later apparent that the outbreak had ended before these interventions were introduced. The investigations revealed faults in the design of the ventilation system.
一次军团病大爆发与斯塔福德地区综合医院有关。共有68例确诊病例在医院接受治疗，其中22例患者死亡。另有35例患者被怀疑感染军团病，其中14例在家接受治疗。所有这些患者都在1985年4月期间去过该医院。流行病学调查表明，在门诊部（OPD）感染该病的风险很高，但医院其他区域没有风险。从其中一个空调设备的冷却水系统中分离出嗜肺军团菌血清1型、庞蒂亚克1a亚群的流行菌株。该设备为医院的几个科室提供服务，包括门诊部。冷却塔和冷却进入门诊部空气的冷水机组中的水被军团菌污染。细菌学和工程学调查显示了冷水机组可能是如何被污染的，以及在冷水机组下方的U形弯管中是如何产生含有军团菌的气溶胶的。这些结果，连同流行病学证据，表明冷水机组很可能是此次疫情的主要源头。近三分之一的医院工作人员有军团菌抗体。这些工作人员可能在由受污染的空调设备通风的医院区域工作，但不一定是在门诊部。有证据表明，这些工作人员中有一小部分患有轻度军团病，并且这些“流感样”疾病在5个月的时间里传播开来。这一发现的一个可能解释是，来自冷却塔源的少量气溶胶可能进入进气口，并分布在该通风系统服务的医院区域。随后发现冷却塔池塘中存在后来被认定为流行菌株的军团菌，因此工作人员有可能在几个月内接触到低剂量的受污染气溶胶。文中描述了控制措施，但后来发现疫情在这些干预措施实施之前就已经结束。调查揭示了通风系统设计中的缺陷。
