In this lecture, we turn to consider the impact of infectious diseases on the health of adolescents. Global progress in reducing under five mortality since 1990 has been very significant. Over this time, the estimated annual number of under five deaths has fallen from 12.6 million to 6.6 million as shown on the left-hand graph here. This is consistent with the under 5 mortality rate declining by nearly half from 90 deaths per 1,000 live births in 1990, to 48 per 1,000 in 2012. And if we put that another way, 17,000 fewer under five children died each day in 2012 than they did in 1990. As you can see in the right hand graph there have been less impressive improvements in rates of infant and neonatal mortality. With around 44% of deaths in children under five occurring during the neonatal period, the first month of life, and nearly three quarters occurring in the first year of life. And of the 6.6 million, under 5 deaths in 2012, most were from preventable infectious causes such as pneumonia, diarrhoea, or malaria. Many under five deaths occur in children already weakened by under nutrition, an equally preventable condition, which is a contributing factor in around half of global under five deaths. The causes of under five deaths vary by national income level. While preventable infectious diseases are still the greatest cause of undefined mortality in low income countries, their share diminishes with higher levels of national income. As you can see by comparing the left hand and right hand pie charts. But I've shown these data here today because many of you will know figures like this very well. So it's your turn now. How significant do you think infectious disease deaths are in adolescents? What types of infectious diseases do you think affect young people? Despite the epidemiological transitions taking place globally, infectious disease also remain among the leading causes of 10 to 19 year old mortality. In addition to mortality from HIV AIDS, lower respiratory tract infections rank among the top five causes of adolescent deaths in all regions, except for high income countries, and the Western Pacific region. Infectious disease deaths are especially high in younger adolescents aged 10 to 14 years. Diarrhoeal diseases are also an important cause of mortality, again particularly in 10 to 14 year olds, where they were the second leading cause of death, while lower respiratory tract infections were the fourth leading cause of death in 10 to 14 year old's. In the same age group, lower respiratory infections, diarrhoeal disease, and meningitis together account for 21%, 18%, and 16% of all deaths in the African, Southeast Asia, and Eastern Mediterranean regions respectfully, a very significant proportion of all deaths. What is particularly worrying is how little we know about, for example the causes of pneumonia and diarrhoea in the adolescent age group. Are these the same types of organisms as seen in younger children? Probably not. Is it the same pattern of diarrhoea that we see, for example? We think not, wondering if perhaps chronic diarrhoea is a greater contribution to mortality than in younger children. Much more research is warranted before we can understand the value of particular interventions in adolescents. But the problem is only made visible when data is broken down by age, as it is in these graphs that were prepared for the WHO Health for the World's Adolescents Report. Tuberculosis, or TB, is now considered a global emergency causing high morbidity and mortality, especially in sub-Saharan Africa. While vaccination against TB using the Bacillus Calmette–Guérin vaccine or BCG as we call it in neonates, has led to a reduction in the incidents of severe childhood tuberculosis. Despite BCG immunisation, TB continues to emerge in adolescents as well as adults. This implies that the current vaccine has limited efficacy against TB in adolescents and adults. This may reflect that the immune response against mycobacterium tuberculosis, the bacteria responsible for TB, is less effective in adolescents. The risk of developing TB, following infections, starts to rise from 12 to 19 years, particularly in males. This is most likely due to changing social mixing patterns among adolescents, resulting in increase contact with infectious tuberculosis cases. However we have inadequate country data about this. Why? Because in most countries data about TB in older adolescents, is aggregated with adult data, with limited adolescent specific information. This makes it very hard to appreciate the extent of tuberculosis infections in adolescents and in young adults. An important point to keep in mind is that adolescents benefit from immunisation strategies that target younger children. In this regard, measles immunisation in children is a major success story for the health of adolescents. For example, in the African region, mortality from measles fell by 90% between 2000 and 2012 in ten to nineteen year olds. However, substantial numbers of adolescents still die from diseases that have been successfully addressed in younger children. Adolescence is also a time where either booster doses or new vaccinations are important. Clearly vaccination against the papillomavirus, the virus responsible for cervical cancer and anogenital warts, is an important vaccine that is administered in early adolescence. Genital HPV is a very common sexually transmitted infection, which usually causes no symptoms, and goes away by itself, but can sometimes cause serious illness down the tract. It affects both men and women, with around four out of five sexually active people having at least one HPV infection in their lifetime. Most people are infected within a few years of first becoming sexually active. Indeed, it's so common that it's described as the common cold of the genital tract. The virus is spread through intimate contact with genital skin during sexual activity, usually from a partner who is unaware that they have an infection. Condoms only provide some protection from HPV as they don't cover all of the genital skin. HPV is responsible for almost all cases of cervical cancer, and cervical cancer is the fourth most common cancer in women. In 2012 there were an estimated number of just under 300,000 deaths from cervical cancer worldwide. Nine in 10 cervical cancer deaths occur in less developed countries. High income countries have lower mortality due to better screening programs, such as regular pap test in adult women. HPV also causes genital warts together with a range of other anogenital cancers such as, vulvar and penile cancer, and other cancers such as those affecting the head and neck. The HPV vaccine is highly effective against the common types of HPV that cause disease. Immunisation is recommended in early adolescence, at 12 to 13 years of age in most countries. In those countries that have effectively implemented population vaccination programs, such as Australia's school-based programs, reductions in cancer are already being seen. Adolescence is also an important time for wider preventive strategies, such as those that aim to contain malaria infections. Like TB, malaria in adolescence has been overshadowed by the huge burden of disease in children less than five. Malaria as you would know is a disease of the tropics and subtropics. It's an infectious disease caused by the parasitic infection of red blood cells by plasmodium which is transmitted by the bite of infected anopheles mosquitoes. In other words, the mosquito is a vector of malarial transmission from which mosquito control can effectively reduce it's incidents. In addition to mortality, the human and economic costs of poor quality of life, health consultations and treatments including hospitalizations are very significant at all ages. The extent of Malarial infection in adolescents has been poorly studied, so we do not have a good understanding of the burden of disease, and the consequences of infection in this age group. In adolescence, in addition to the risk of death, we are also concerned about the effects of Malaria and in particular anemia on education and learning. Malaria infection contributes to school absenteeism, poor academic performance and therefore school drop out. 90% of the worlds malaria occurs in sub Saharan Africa, where around 500 million cases are reported annually. These figures show those regions where adolescents are most affected by malaria. You can see that Africa's particularly problematic, 16.5% of adolescent deaths in Africa are estimated to be due to malaria. But even within the one region, the same region, there are widely differing rates of malaria in adolescents. It's estimated that 50% of Nigerians, for example, experience an episode of malaria every year. The age of incidence of malaria varies with the intensity of transmission. This is because susceptibility to, severity of, and age distribution of malarial disease depend on the acquisition of immunity, which is strongly related to the intensity of transmission. Where transmission is intense, clinical disease is most common in young children, as seen on the lower part of this panel. Immunity develops with increasing age, and adolescents and adults are far less affected in these types of communities. In contrast, in areas of lower transmission such as the upper panel, clinical disease occurs throughout life and is more likely to affect adolescents. However, in addition to the universal interventions, for example, of mosquito control, the instance of malaria also reflects the extent that individual approaches are utilized by adolescents. Studies continue to show significant gaps in adolescent knowledge about specific aspects of prevention of malaria with low rates of uptake of insecticide treated bed nets by adolescents in many communities. There is every opportunity for media, for schools, and for health services to function more actively, as a source of health promotion around malaria control targeting adolescents. A study of adolescent knowledge of treatment and prevention of malaria, in an endemic coastal region in Nigeria, showed widespread opportunity for improved understanding of the methods for preventing malaria, as you can see here on the left. Only 70% of school aged adolescents were aware, that a insecticide treated nets kill mosquitoes, and only 25% percent were aware that bed nets is the main method of preventing malaria. Less than 10% of the sample had ever actually slept under a bed net, and remember, this study was in an endemic area. On the right, from the same study of 400 adolescents at secondary schools, we can see the main source of information about malaria prevention. Over half reported that various mainstream media, for example radio, TV, newspapers, were the most common source. Less than a third reported their main source of information was from either teachers or healthcare providers, which suggests obvious avenues for improvement. In many African communities adolescents are now the most educated in their community. Promoting adolescent knowledge and behaviors has also been argued as providing an important entry into the education of the entire community.
