All of the above are urgently needed in developing nations. A major barrier to achieving these improvements is the underlying weakness of health systems in resource-poor countries, including a shortage of health workers and a lack of disease surveillance programs.

All of the above are urgently needed in developing nations. A major barrier to achieving these improvements is the underlying weakness of health systems in resource-poor countries, including a shortage of health workers and a lack of disease surveillance programs.

All of the above are urgently needed in developing nations. A major barrier to achieving these improvements is the underlying weakness of health systems in resource-poor countries, including a shortage of health workers and a lack of disease surveillance programs.

The 1918 influenza pandemic is estimated to have killed between 50 million and 100 million people worldwide. Many of those deaths were due to the effects of pneumococcal pneumonia, a secondary complication of flu for which no antibiotics existed in 1918.

The 1918 influenza pandemic is estimated to have killed between 50 million and 100 million people worldwide. Many of those deaths were due to the effects of pneumococcal pneumonia, a secondary complication of flu for which no antibiotics existed in 1918.

The clearing and settlement of tropical rainforests has exposed woodcutters, farmers, and ecotourists to new vector-borne diseases.

The human papillomavirus (HPV) causes more than 90% of cervical cancer cases.

The human papillomavirus (HPV) causes more than 90% of cervical cancer cases.

White blood cells are not a type of infectious agent. Part of the immune system, white blood cells fight infection rather than cause it. 

White blood cells are not a type of infectious agent. Part of the immune system, white blood cells fight infection rather than cause it. 

White blood cells are not a type of infectious agent. Part of the immune system, white blood cells fight infection rather than cause it. 

Someone in the world is newly infected with tuberculosis (TB) every second. In 2008 there were an estimated 9.4 million new cases of tuberculosis and 1.8 million deaths.The vast majority of TB deaths are in the developing world, and more than half of all deaths occur in Asia.

Someone in the world is newly infected with tuberculosis (TB) every second. In 2008 there were an estimated 9.4 million new cases of tuberculosis and 1.8 million deaths.The vast majority of TB deaths are in the developing world, and more than half of all deaths occur in Asia.

An estimated 1.8 million airline passengers cross international borders daily, creating routes by which human infections can radiate around the world within hours.

An estimated 1.8 million airline passengers cross international borders daily, creating routes by which human infections can radiate around the world within hours.

By identifying pathogens in the animals where they naturally live and monitoring those organisms as they move from animals into people, it may be possible to prevent deadly new infections of animal origin from entering and racing through human populations.

In syndromic surveillance, all of the above are used in addition to other patterns that suggest an outbreak. Despite the emergence of this innovative surveillance method, most surveillance still depends on tracking reported infections. 

In syndromic surveillance, all of the above are used in addition to other patterns that suggest an outbreak. Despite the emergence of this innovative surveillance method, most surveillance still depends on tracking reported infections. 

In syndromic surveillance, all of the above are used in addition to other patterns that suggest an outbreak. Despite the emergence of this innovative surveillance method, most surveillance still depends on tracking reported infections.