The use of chlorine as a disinfectant in an ETC

The Ebola virus can survive for a prolonged period on surfaces in the dark1 or at a low temperature for several days and remain infective throughout this period.2 Until recently, there were no studies that investigated the efficacy of chlorine disinfection of the Ebola virus, though numerous studies have demonstrated chlorine's effectiveness against a wide range of other micro-organisms and encapsulated RNA viruses.3–7 Based on expert consensus, the 2014 WHO8 guidelines recommend the use of 0.5% chlorine solution as a disinfectant to clean materials and surfaces and 0.05% chlorine is used in practice to bathe patients and to disinfect the skin of red zone workers while ‘doffing’ (the controlled removal of PPE on exiting in the ETC). This has been standard practice in ETCs during the current West African EVD epidemic. More recent evidence has shown Ebola is destroyed in fewer than 60 s by exposure to 0.5% chlorine solution, although this minimum time can be prolonged markedly when the virus is suspended in an organic soil load. Therefore, it seems likely that the practices of West African ETCs may change in light of this, with the result that exposure to higher concentration chlorine solution will occur for a longer duration in the future as part of normal disinfection and doffing procedures.

Exposure to chlorine solution and gas is a routine risk for EVD red zone workers. Anecdotally, red zone workers describe significant temporal variation in the irritant effect of chlorine gas on their respiratory systems and eyes within the KTTU. Creating a uniform and consistent concentration of chlorine solution throughout the facility is challenging; for practical reasons in the ETC, the chlorine solutions are hand-mixed centrally then piped to reservoir barrels (Figure 1) where, depending on usage, they may be used quickly or remain for up to a day.9 Although on occasions, higher chlorine solution concentrations than intended have been detected at the KTTU, frequent unequivocal variation in the concentration of chlorine solution has been difficult to prove; it is likely that other factors, such as environmental conditions, exposure type and duration are also important to how the exposure is perceived, for example, anecdotally, there often appears to be significant off-gassing of higher concentrations of chlorine gas when the taps are first opened. Over the same 2-month deployment, in excess of 30 other red zone workers from the same facility presented to primary care with minor, self-limiting symptoms consistent with mild inhalational chlorine exposure.

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Figure 1

Photograph of the interior of the Kerry Town Ebola Treatment Unit with a chlorine solution sprayer (A) and one of the barrels (B), tap painted with the word ‘Hi’ to show it contains 0.5% chlorine solution. These were similar to those used by the patient in this case.

Pathophysiology and symptoms of chlorine inhalation injury

The respiratory tract, due to its large mucosal surface area, is particularly susceptible to injury from chlorine. The degree of toxicity is dependent on chlorine's chemical and physical properties, the concentration of the fumes and the duration of exposure.10 Acute exposure to chlorine and associated fumes can cause a spectrum of clinical conditions, ranging from reactive airways dysfunction syndrome, to adult non-cardiogenic pulmonary oedema and even death.11

Chlorine gas (Cl₂) and hypochlorous acid (HOCl) are the most prominent reactive chlorine species in aqueous solution, and both are known to cause epithelial injury. The biochemical mechanism for this epithelial injury is postulated to be direct oxidative injury, with activation of the inflammatory cascade resulting in neutrophilia in the acute stages, further contributing to damage.11 This can result in acute conditions, as outlined above, but also late-developing complications: mucosal hyperplasia, subepithelial fibrosis, bronchiolitis obliterans and airway hyper-responsiveness.12 In the case described here, the airway hyper-responsiveness was a type of irritant-induced non-immunological asthma with acute phase neutrophils as the mediator, explaining the poor response to steroid therapy.

Although detectable to human beings at 0.1–0.3 parts per million (ppm), chlorine gas does not become irritating until concentrations reach 1–3 ppm.13 The WHO14 Task Group on Environmental Health Criteria for Chlorine and Hydrogen Chloride suggests a workplace exposure limit of 1 ppm for up to 15 min. When the clinical effects of inhalation are compared with the effects of known concentrations of chlorine fumes, the off-gassed fumes from taps in the facility suggest a concentration of approximately 30 ppm (Table 1).

Prehospital care for chlorine exposure should include decontamination of the patient's skin and eyes as well as removal of contaminated clothing.13 In rare cases where chlorine burns are present, they should be treated similarly to thermal burns. Evacuation of the patient to a well-ventilated area is the appropriate prehospital care for chlorine inhalation. Common symptoms of acute chlorine inhalation above 15 ppm include dyspnoea with an irritating cough and wheezing, eye and throat irritation, lacrimation, rhinorrhea, substernal pain, nausea, vomiting, headache, dizziness and syncope. Findings of rales or crackles on physical examination, as well as decreased SpO₂, can be indicative of more serious injury including acute respiratory distress syndrome (ARDS) or pulmonary oedema; these may ultimately progress to an obliterative bronchiolitis.15 Hyperchloremic metabolic acidosis has also been described.16

In cases where there is a serious risk of late complications, management with humidified oxygen and admission for observation is appropriate. Non-humidified oxygen can act as an airway irritant and should be avoided. A baseline chest radiograph should be obtained and respiratory function monitored, including arterial blood gases (ABGs) and pulse oximetry. A limitation of clinical investigation in an ETC is that radiological investigations are impossible; in this case the radiograph was only performed once the patient arrived at the role 2 facility. Even asymptomatic patients may require hospital admission to monitor for late-evolving complications, especially in the cases of children, those with pre-existing respiratory or cardiac comorbidities, and people who have had exposure to high concentrations of chlorine. In severe cases of exposure resulting in significant pulmonary oedema and type 1 respiratory failure, continuous positive airway pressure ventilation should be considered.

The risk caused by chlorine inhalation injury in an ETC

In contrast with many other circumstances where there is a risk of chlorine inhalation, an ETC presents particular difficulties, including extracting and decontaminating an injured healthcare worker (HCW). Common situations, which might result in chlorine inhalation, such as exposure at a swimming pool or an industrial spill, require extraction to a well-ventilated area, and in most cases, the chlorine is the only significant situational hazard; however, extraction and care after chlorine inhalation injury in an ETC has more parallels with chemical, biological, radiation and nuclear warfare scenarios with a requirement for specially trained staff to safely extract the injured person, while minimising the risk of exposing the patient and rescuers to inadvertent Ebola exposure. The use of respirators in the red zone was considered to protect against chlorine exposure; however, there were concerns about increased HCW degradation in the tropical environment as well as difficulties with safe removal and decontamination of respirators after use. In the case presented here, the casualty was able to safely self-extract prior to his collapse, which significantly decreased the risk to him and his caregivers; in other situations, this might not be possible. Minimising the likelihood of dangerous chlorine inhalation leading to symptomatic episodes, such as in this case, should be a paramount concern for ETC managers. When the KTTU was conceived, operating procedures were designed for these potential situations, and were regularly reviewed17 ,18 with the predicted extraction scenarios regularly rehearsed. Constructing distribution systems for chlorine solution that accurately and consistently deliver the appropriate concentration to the end user are also an important consideration when designing an ETC. Future ETC constructions could also consider the possibility of air extraction or ventilation capabilities to minimise the noxious effects of chlorine fumes; however, this could be difficult to achieve due to concerns of aerosolising Ebola virus within the ETC.