How might an increase in population lead to more disease outbreaks.

Fertility, migration and urbanization affect the spread of diseases. Increased population densities and unhealthy living conditions in urban slums can ease the transmission of infections. Migration may also increase vulnerability to disease.

With a higher population there are more people to have chances at getting sick. Now once someone gets sick most people are bunched up in cities meaning there in contact with a lot of others making the disease spread quickly.