In adults, 94% of absorbed lead is deposited in the bones and teeth, but children only store 70% in this manner, a fact which may partially account for the more serious health effects on children. The half-life of lead in bone has been estimated as years to decades, and bone can introduce lead into the bloodstream long after the initial exposure is gone. The half-life of lead in the blood in men is about 40 days, but it may be longer in children and pregnant women, whose bones are undergoing remodeling, which allows the lead to be continuously re-introduced into the bloodstream. Also, if lead exposure takes place over years, clearance is much slower, partly due to the re-release of lead from bone. Many other tissues store lead, but those with the highest concentrations (other than blood, bone, and teeth) are the brain, spleen, kidneys, liver, and lungs. Lead is removed from the body very slowly, mainly through urine. Smaller amounts of lead are also eliminated through the feces, and very small amounts in hair, nails, and sweat.Lead has no known physiologically relevant role in the body, and its harmful effects are myriad. Lead and other heavy metals create reactive radicals which damage cell structures including DNA and cell membranes. Lead also interferes with DNA transcription, enzymes that help in the synthesis of vitamin D, and enzymes that maintain the integrity of the cell membrane.
The risk of developing Haemophilus meningitis is most directly related to an individuals vaccination history, as well as the vaccination history of the general public. Herd immunity, or the protection that unvaccinated individuals experience when the majority of others in their proximity are vaccinated, does help in the reduction of meningitis cases, but it does not guarantee protection from the disease. Contact with other individuals with the disease also vastly increases the risk of infection. A child in the presence of family members sick with Haemophilus meningitis or carrying the bacteria is 585 times more likely to catch Haemophilus meningitis. Additionally, siblings of individuals with the Haemophilus influenzae meningitis receive reduced benefits from certain types of immunization. Similarly, children under two years of age have a greater risk of contracting the disease when attending day care, especially in their first month of attendance, due to the maintained contact with other children who might be asymptomatic carriers of the Hib bacteria. Diagnosis
Prevention
Before the widespread use of the Hib vaccine, Haemophilus meningitis accounted for 40%-60% of all meningitis cases in children under the age of fifteen, and 90% of all meningitis cases in children under the age of five. Vaccination can reduce incidence. Vaccination has reduced the occurrences of Haemophilus meningitis by 87-90% in countries with widespread access to the Hib vaccine. Rates are still high in areas with limited levels of vaccination.