Main risk factor clusters

• WASH 2 10–23: Water, sanitation and hygiene are central elements to limit the risk of communicable diseases in populations experiencing an emergency. As such, they are also central to CHEs and often in a more precarious state than in other emergencies. WASH risk factors include issues such as lack of safe drinking water,2 10 12 14–17 19–21 lack of hygiene,10 15 19 22 hygiene behaviour,18 21 22 lack of soap,2 19–21 24 lack of bed nets25 ,20 (as vector control is usually seen as a part of WASH in humanitarian response) and general water scarcity,2 10 12 14–17 19–21 as well as lack of adequate sanitation and latrines. These factors considerably increase the risk for diarrhoeal diseases and compound risks for other types of communicable diseases especially if they are coupled with other risk factor categories such as overcrowding and mass population displacement.

• Overcrowding 2 10 13 15 17–20 22–24: Overcrowding in CHEs is usually a function of either mass population displacement or entrapment. While overcrowding can also be an issue in ad hoc shelters after the widespread destruction of homes and infrastructure, it is more prevalent if populations are forced to become refugees or internally displaced persons and are forced into camps. Overcrowding affects both hygiene-related diseases, such as diarrhoeal diseases, but also increases the transmission rate of diseases such as measles and other infections that spread from person to person.

• Mass population displacement 2 10 12 14 15 17–20 23 24 26–34: Mass population displacement is a trigger for most risk factor categories and as such possibly the main risk factor in CHEs. Mass population displacement is usually associated with large numbers of people moving into camp settings, often associated with overcrowding, inadequate shelter and poor WASH conditions.2 10 15 17–20 29 Additionally, populations are displaced into regions and areas with insufficient resources and services and with potentially increased contact of naive populations with new disease vectors. Early camp structures (such as layout of tents and siting of toileting areas) can lead to further complications. Early layout often develops as an ad hoc response to mass population displacement but may prove completely unsuitable as the camp expands.

• Nutrition 2 10 12 13 15 17 19 20 22–24 34: While nutrition factors such as malnutrition,2 10 13 15 17 19 20 22 24 34 food shortages2 10–12 17 19 and exposure to contaminated food19 20 are mainly risk factors at the individual level, they also pose increased risk to populations as a whole if a sufficient percentage of the population is exposed. Nutrition factors are related to increased susceptibility to communicable diseases with resulting greater shedding and transmission to others. At the population level, nutritional factors can exacerbate other risk factors and risk factor clusters, for example by increasing the risk of violence and social unrest. Root causes for nutrition risk factors lie mainly in other risk factor clusters such as insecurity and armed conflict or mass displacement and inadequate humanitarian response.

• Living conditions 2 12 19 20 23: Poor living conditions are a combination of inadequate shelter, overcrowding and other individual factors in the immediate surroundings of an individual or group of individuals. A  key risk for people uprooted from their normal lives in CHEs and subject to inadequate resources and shelter is indoor air pollution.2 19 20 This is due to indoor fires, both for cooking purposes and for heating.2 19 20

• Insecurity 2 10 14 19 23 28 30 31 33 35: Insecurity is a multifaceted bundle of risk factors that is one of the main root causes for increased mortality (all causes) in complex humanitarian emergencies. Insecurity is composed of factors such as armed conflict,10 social disruption10 19 30 33 and political instability.2 The specific nature of insecurity differs from complex emergency to complex emergency. However, by our (UNOCHA) definition, most, if not all, complex emergencies experience a high level of severe violence either from inter-state or from intra-state conflict. Insecurity triggers other factors such as a lack of an adequate humanitarian response as it poses risks to aid workers and inhibits access to beneficiaries. Additionally, it also inhibits access for the population to health services and has a high potential to disrupt all other services.

• Infrastructure 2 18 19 22 23 31: Due to insecurity and also in some cases long-term neglect and lack of funding, infrastructure in CHEs is often inadequate, especially in response to mass influx of people either in camps or in the community. Lack of infrastructure also often comes with a lack of domestic coordination,2 19 31 which additionally inhibits efficient coordination with international response. A lack of resources,2 31 water,2 10 12 14–17 19–21 electricity,19 funding22 and staff22 makes the affected population more dependent on an international response.

• Humanitarian response 10 12 26 34: By our (UNOCHA) definition, a complex emergency demands a multifaceted, multiagency international humanitarian response. However, poor response can itself become a risk for the spread of communicable diseases. Problems can lie with the response itself, due to a lack of international commitment or a lack of professionalism of the responding agencies and organisations.12 Problems can also arise domestically due to restrictions by governments or warring parties, unsafe conditions in which aid workers cannot properly work without unacceptable levels of risk for themselves or lack of access for various reasons.10 34 This also includes lack of organisational motivation22 and poor institutional support10 and complex international issues such as the lack of a binding legal framework for the protection of internally displaced populations.24

• Environment 2 12 15 19–21 23 34: Environmental factors can increase the likelihood of communicable diseases outbreaks, and this is true beyond the context of CHEs. However, many environmental factors, which would not have mattered otherwise, can be triggered by mass population displacement, especially if populations are displaced into areas with a higher prevalence of environmental risk factors. Environmental risk factors include weather and climate factors, such as cold and dust storms,2 20 but also vector habitats,19 20 34 increased contact with animals19 20 and endemic diseases.2 12 19 Mass population displacement potentially puts people at risk from these factors and also exacerbates the factors themselves due to the additional stress placed on the local environment by camps and by an influx of large numbers of people, often accompanied with significant land use changes.19

• Economy 2 19 23 25 27 30 31: While economic factors such as poverty and lack of resource are certainly issues that are important in humanitarian emergencies, they are not of the highest importance in CHEs. Poverty and economic degradation have the ability to further exacerbate the root causes of the underlying conflict but only indirectly increase the likelihood of communicable disease outbreaks.

• Health and public health services 2 10 12–15 17 19 20 23 24 27–29 31–36: Breakdown of health and public health services is probably one of the main risk factors for communicable diseases in CHEs both for individuals and for populations. Lack of access to health and medical care is a key risk factor for severe progressions of most communicable diseases for the individual.2 10 12 15 17 19 20 28 29 31 33 34 It also facilitates the further spread of communicable diseases such as tuberculosis and makes detection of cases and outbreaks harder. Additionally, in complex emergencies, public health services including vaccination, communicable disease prevention and control measures, and surveillance are no longer available making disease outbreaks more likely, harder to detect and harder to control.2 10 12 13 15 17 19 20 24 27 31–33 35 This breakdown of services can be seen as a function of the underlying conflict but is further compounded if there is not enough political will to provide adequate health protection.2

• HIV-specific risk factors 2 10 15 19 28 30 33: HIV is a unique and often overlooked concern in CHEs. While many of the aforementioned risk factors also apply to HIV, there are some very specific additional risk factors that are associated with an increase in the incidence of HIV in complex emergencies. Key risk factors for an increased transmission of HIV include sexual and gender-based violence,2 10 15 19 28 30 33 increased rates of sex work,2 10 19 28 30 33 use of unsafe blood products and conflict-related increased demand for (potentially unsafe) blood products,2 19 28 lack of infection control in healthcare facilities,2 19 28 lack of condoms2 28 and an increased use of illicit drugs.19 28 33 A high sexually transmitted infection prevalence can be linked to an increased risk of contracting HIV.15 Lack of healthcare access and lack of antiretroviral therapy increase the likelihood of vertical transmission,30 and mass population displacement can lead to increased contact (sexual and otherwise) with populations with a higher prevalence.10 28 33

Risk factor cascades

The risk factor clusters as well as individual risk factors often interact and exacerbate one another. Some risk factors and risk factor cluster are particularly likely to start risk cascades, especially mass population displacement (as illustrated in figure 3) and insecurity (as illustrated in figure 4).

• Download figure
• Open in new tab
• Download powerpoint

Figure 3

Mass population displacement cascade. WASH, water, sanitation and hygiene .

• Download figure
• Open in new tab
• Download powerpoint

Figure 4

Insecurity cascade.

One of the key mechanisms for driving risk factors for communicable diseases in complex emergencies is mass displacement (as shown in figure 3), especially mass displacement into camp settings.18–20 Camp settings enforce a high dependence on outside support for the residents. This makes residents more at risk for other risk factors. Mass displacement can reduce access to healthcare and even if access to healthcare is maintained the level and quality might be poor.2 10 15 17 18 Mass displacement thus tends to trigger all risk factors associated with lack of access to healthcare and increases the risks for communicable diseases both at individual and community levels. This is often coupled with living conditions that are conducive to increased transmission of communicable diseases and put the individual more at risk.2 12 19 20 This includes the lack of adequate shelter, which is especially prone to increase vector-borne diseases and respiratory diseases, especially in areas with cold temperatures.2 10 15 17 19 20 24 29 Overcrowding—often together with inadequate shelter and lack of sufficient WASH—increases the likelihood of triggering hygiene risk factors and also the transmission rate of respiratory infections and diseases such as measles. For respiratory infections, this is further exacerbated by conditions that lead to the use of indoor fires and subsequent indoor air pollution.2 19 20

Additionally, as human populations become more overcrowded, transmission of infections becomes more efficient, that is, the reproductive ratio (R₀) of the infection increases.37 As R₀ increases, the threshold immunisation coverage needed to achieve herd immunity also increases.38 Consequently, immunisation coverage that was previously sufficient is inadequate to prevent outbreaks. One of the main problems, especially in overcrowded camps, is the provision of safe water and adequate hygiene. If WASH conditions deteriorate, especially diarrhoeal disease risk increases considerably. Any insufficiency in WASH is more pronounced when coupled with high population density, as experienced in camp situations. However, mass displacement, even when not coupled with displacement into camps, also triggers additional risk factors. Displacement can be into areas with endemic diseases to which the displaced population has no immunity.12 Additionally, mass displacement makes populations vulnerable to environmental factors as well as reinforcing these.12 21 Mass displacement can exacerbate insecurity and therefore reignite a vicious circle leading to further displacement and breakdown of healthcare, services and infrastructure.

Insecurity itself, whether exacerbated by mass displacement or not, is an important triggering mechanism for communicable disease risk factors in CHEs (as shown in figure 4). Insecurity, including political instability, armed conflict and social disruption, destroys services that previously prevented the spread of communicable diseases or disallows access to these services by making accessing them unsafe.2 10 14 19 28 30 31 33 36 39 40 This is particularly important for healthcare services that in the last few years have increasingly become a target of armed conflict and attacks, decreasing the safety of both staff and patients.41–43 Additionally, disease prevention programmes are likely to be disrupted and infrastructure to be destroyed.15 17 20 36 With regard to humanitarian response, which can under certain circumstance step into the place of previously government-provided services, insecurity makes an adequate humanitarian response difficult.10 34 Not only will access to affected populations be difficult, especially in situations when insecurity and active fighting lead to entrapment or even to siege situation, as recently seen in Syria and Iraq, but insecurity also poses risks to aid workers’ security both for domestic/national and international/expatriate staff.10 34 Aid organisations are—understandably—increasingly reluctant to accept very high risks to their personnel, leading to gaps in provision of services, which would otherwise have been filled by a humanitarian response. Insecurity also increases the risk of the loss of domestic experts in disease prevention due to injury, death and flight.42

These are only some aspects of two of the many mechanisms by which CHEs drive risks for communicable diseases. We identified further cascades triggered by economics and infrastructure and risk factor cluster interaction for WASH and health systems risk factors. However, the level of complexity in these types of emergencies makes it impossible to capture all levels of interaction adequately. It is not so much that complex emergencies create different risk factors than other humanitarian crises but that they exacerbate any individual risk factors and compound interaction effects. Levels of risk factors will invariably be higher in a complex emergency and the amount of interacting risk factors creates a ‘perfect storm’44 where a multifaceted, well-funded and logistically and politically highly integrated humanitarian response is not possible due to political, financial or security reasons. These conditions make the danger of one or more outbreaks of communicable diseases extremely high.

While complex humanitarian emergencies do not trigger risk factors that are unknown in other types of emergencies and disasters, they produce much higher levels of risk and often tend to trigger more of the known risk factors as well as risk factor cascades. Risk factors related to poor sanitation and hygiene,45–52 nutrition,46 53–55 mass population displacement and overcrowding47 53 56–60 have been discussed extensively in the academic literature as being important in most types of emergencies, while risk factors resulting from an inadequate humanitarian response, armed conflict and a breakdown in government services are generally more associated with complex emergencies and other situations linked to failing statehood, such as civil war.

The question remains of how to make useful this information on risk factors and their interactions. While many of the risk factors and even starting points of risk factor cascades are addressable, the context of a complex emergency often prevents any such interventions. A key first step in any attempt to address these issues in a given complex emergency is a rapid but thorough initial needs assessment,3 61–63 including an assessment of the most critical risk factors present in that specific complex emergency in order to develop an evidence-based intervention strategy. However, it is unclear how to best undertake such a needs assessment. Moreover, beyond the development of evidence-based risk assessment and management methods, there is a need for more rigorous research into the operational and structural barriers that make it difficult to address risk factors in CHEs.

Limitations

This systematic review included subjective interpretation as risk factors were rarely the main focus of the included articles. Authors do not always clearly describe the risk factors and their mechanisms. This introduced an interpretative and subjective element within the included articles, which became more subjective due to the level of interpretation required to complete the thematic synthesis. However, the authors maintained constant feedback to one another and discussed challenges, interpretations and limitations to ensure reliability and validity of the findings to the degree that a qualitative analysis allows. We are therefore confident that our interpretation properly reflects the data, although agreeing that other interpretations are possible and may be equally valid. This review was necessarily a qualitative synthesis as the evidence base (heterogeneous and qualitative in nature) did not support quantitative analysis.