Neonatal sepsis is a blood infection that occurs in an infant younger than 90 days old. Early-onset sepsis is seen in the first week of life. Late onset sepsis occurs after 1 week through 3 months of age. Causes: Neonatal sepsis can be caused by bacteria such as Escherichia coli (E coli), Listeria, and some strains of streptococcus. Group B streptococcus (GBS) has been a major cause of neonatal sepsis. However, this problem has become less common because women are screened during pregnancy. The herpes simplex virus (HSV) can also cause a severe infection in a newborn baby. This happens most often when the mother is newly infected.The populations of many regions are rapidly growing older. The process of population aging is a major success story, which began unfolding only at the end of the twentieth century. Demographers define population aging as an increasing median age of a population or an alteration in the age structure of a population, so that elderly persons are increasingly represented within a country's overall age structure. The economic and social consequences of aging are considerable, particularly with regard to the increasing burden of dependency. These consequences in the industrialized nations of Europe and North America have been well publicized. However, less is known about the effects in less well developed regions. Older populations in many developing countries are growing more rapidly than are those of industrialized nations.