During 1950-2008, the proportion of the world's population living within cities grew from 33% to 50% (1). The number of cities with >10 million people grew from 3 to 20 over the past 30 years; 15 of these ‘megacities’ were in the developing world (1). The urban population in sub-Saharan Africa is expected to triple between 2010 and 2050 to >1.2 billion people (2). This process of massive urbanization has been ongoing in many developing countries, including in sub-Saharan Africa where urbanization rates, often linked to extreme poverty (3), are the highest in the world (4). Perceived opportunities for improving the family status and for education have led many people to leave rural settings in favour of urban living environments which can be more challenging and less familiar (5). Since urban areas often cannot address the demands of an expanding population with strengthened infrastructure, the new residences are frequently seen within informal settlements, often referred to as slums, where the density of population is high, and sanitation, availability of clean water, and health services are low (5).

Due to various adverse conditions prevalent in informal settlements, transmission of pathogens that cause infectious diseases may be facilitated, resulting in life-threatening syndromes, such as severe pneumonia, diarrhoeal disease, and febrile illnesses. To identify the emerging pathogens, characterize their epidemiology and the burden of disease, and assist in identifying priorities for the prevention of diseases, the International Emerging Infections Program (IEIP) of the Centers for Disease Control and Prevention (CDC), in collaboration with the Kenya Medical Research Centre (KEMRI), established a surveillance for key infectious disease syndromes and their aetiologies. This surveillance takes place in two villages—both within Kibera, an informal settlement, representing one of the largest contiguous slums in sub-Saharan Africa (6). The area is characterized by high density of population, poor sanitary conditions, and limited access to safe water (7).

Healthcare-use patterns determine whether a clinic or hospital-based surveillance is adequate to define the incidence of diseases or whether more active approaches, such as periodic home-visits, are needed to identify a substantial proportion of illnesses. To better understand the healthcare-seeking patterns of the population under surveillance, we carried out a healthcare-use survey (HUS) within the Kibera surveillance area. Such studies can help interpret data from disease-surveillance systems, especially among people for whom delivery and quality of health services are poor (8). They provide baseline information about syndromes of substantial morbidity and mortality and can yield a method to extrapolate the burden of disease using the proportion of illnesses missed when surveillance is dependent upon attendance at a health facility. Such data improve precision in estimates of disease-incidence rates when relying on clinic-based surveillance. We set out to estimate the proportion of people with pneumonia, diarrhoea, or febrile illness symptoms, who seek care inside and outside the Kibera informal settlement and to define the places where care is sought. We also sought to characterize factors associated with specific healthcare-seeking behaviours and to identify key barriers to accessing care.

Massive urbanization has led to crowded residential communities with poor sanitation, water and air quality. This has resulted in various stresses on health systems with potential implications on disease-incidence rates and rapid spread of recognized and emerging infectious diseases. Because of this potential, we have established a population-based surveillance for key infectious disease syndromes and their aetiologies in Kibera, a large urban slum in East Africa. This healthcare-use study has provided baseline data for this surveillance programme of infectious disease syndromes.

The findings of the study suggest that a high proportion of illnesses in this urban setting is associated with some form of healthcare-seeking, often including informal kiosks or unlicensed care providers. However, a substantial number of patients, regardless of age, living within informal settlements do not appear to use the multiple licensed healthcare-delivery options available within urban environments. This is consistent with the recent findings of another study of informal settlements in Nairobi (9). However, the proportion of patients accessing healthcare facilities in our study was higher for diarrhoeal disease and for fever (but not for respiratory diseases in under-five children) than that reported from a rural area in Kenya during a healthcare-use study conducted around the same time (10).

Healthcare-use was not significantly different among the two age-categories (under-five children and older children and adults aged ≥5 years), although under-five children are often at special risk of serious outcomes from illness. The results are not in agreement with that from another slum setting in Nairobi, which showed that infants were prioritized by caretakers for healthcare when compared with older children (11). Despite being an impoverished population, most people sought some sort of healthcare for illness outside the home. Although the majority of the patients visited licensed clinics and hospitals, >35% of the patients with respiratory, febrile or diarrhoeal illness only visited chemists (pharmacists) and unlicensed kiosks selling drugs or other unlicensed care providers instead of licensed clinics. Reasons given for not seeking healthcare suggest inability to meet costs, along with inconvenience. These findings have important implications for the delivery of healthcare and for public-health interventions. These also suggest that comprehensive surveillance for infectious disease syndromes and emerging pathogens in an urban setting would either need to include a large number of clinics, hospitals, and kiosks and informal care providers, or would require community-based approaches, or ideally, a combination of the two.

While most (85%) people sought some sort of healthcare, the most common reason reported for not seeking healthcare was cost. The Kenya National Health Accounts for 2002 (published in 2005) indicated that households paid for 51% of all healthcare costs, and per-capita annual health costs were about Ksh 1,500 (US$ 19 in 2002) (12). Given that >55% of the Kenyan population is classified as ‘poor’, cost likely represents a substantial barrier to appropriate levels of healthcare. In fact, the same survey found that about one-third of ill people classified as ‘poor’ did not seek healthcare compared to 15% of the better-off (12). The implications for our surveillance activity are as follows: to optimize detection of illnesses (so that the disease can be characterized and specimens collected and tested), health services would need to be provided without consideration of cost to the population under surveillance.

The span of time a caretaker spends in the home with children was associated with lower healthcare-use for under-five household members, especially when the caretaker is always at home. We cannot confidently explain this finding. Perhaps, such caretakers are not being able to seek healthcare outside the household for one child because they cannot leave the house due to other children who must be cared for. However, not having anyone available to take care of other children was only cited as a reason for not seeking healthcare in less than 1% of the time. Another possibility is that women who were always at home were less likely to have income and to have available funds to pay for care. Alternatively, caretakers who are always at home may be serving as a healthcare-use ‘proxy’, able to monitor the child's status in the home, and only seeking healthcare when the condition worsens.

Over the next two decades, the urban population within the developing world is expected to grow by nearly three billion while the rural population is projected to increase by nearly 500 million (1). Urban migration has been particularly pronounced in Africa (1) where perceived opportunities for generation of income and education have encouraged mobility at the expense of key factors, such as sanitation, hygiene, and dense population, which can impact the quality of life. Urban centres often do not have the infrastructure to handle the influx of people spawning informal settlements which have expanded rapidly in many cities in Africa. From 1971 through 1995, the share of Nairobi residents residing within informal settlements increased from roughly one-third to >60%, representing a population increase from 167,000 to nearly two million (13).

The findings of this survey suggest that diarrhoeal, respiratory and febrile illnesses occur commonly in Kibera and that while under-five children appear to be at particularly high risk of illness, there is also substantial morbidity among older children and adults. We cannot characterize the incidence rates of these syndromes based on this survey since its timing (mid-July) does not allow seasonality to be taken into account. Active surveillance which began in 2006 will provide more reliable data on the incidence of key infectious disease syndromes and their aetiologies and the ability to characterize the risk factors and transmission patterns for specific pathogens. The findings of this study suggest the need for a community rather than facility-based design to achieve our objectives for systematic disease surveillance in this setting, given the high proportion of illnesses not associated with visit to a healthcare facility (and a large number of various types of healthcare facilities available within this urban environment)

The ‘self-reporting’ nature of the study likely led to misclassifications of illness, especially for pneumonia and fever. For example, while the assessment of diarrhoea is fairly straightforward, the assessment of fever is more subjective, especially when thermometers are rarely used. ARI is even more subjective as the case definition of ‘cough and difficult breathing’ does not necessarily exclude upper respiratory tract infections or bronchitis. Such non-specific measures have the potential to bias estimates of prevalence upward and potentially blur the relationships between valid syndromes and associated appropriate healthcare-use.

As noted above, the findings of this study conducted within an urban informal settlement differed from a similar study in 2005 that we conducted within a rural Kenyan area (10). Within the rural setting, distance of residence to healthcare facilities played a much larger role in healthcare-seeking behaviour. While the proportion of patients accessing clinics and hospitals for diarrhoeal disease and fever was higher in the urban setting, both studies confirmed that facility-based disease surveillance (without other components to access patient information and relevant specimens) would substantially underestimate the burden of diseases due to specific aetiologies. In addition, the proportions of the respondents and children reporting diarrhoeal and respiratory diseases (but not febrile illness) were higher within the urban area, possibly suggesting an impact of densely-populated environments with sub-optimal sanitation but also potentially influenced by different tendencies to recognize and/or report an illness in urban versus rural areas. Confirmation and characterization of differences and similarities will await results of active, comprehensive, community-based surveillance now ongoing within villages in Kibera and in rural western Kenya. In addition to implications for surveillance methodologies and interpretation of surveillance data, the findings of the present study suggest that strategies are needed to ensure that the massively-increasing number of urban residents has optimal access to medical care and treatment.

The authors are grateful for the work of the community interviewers and other KEMRI-CDC staff who work in Kibera, the administrative support of Evelyne Mulama, and the continuing cooperation and support from the people of Gatwikera and west Soweto in Kibera. This paper is approved with the permission of the Director KEMRI.