There was still plenty of typhoid fever in the US during the second period which starts out "spikey" and eventually takes the shape of a moderately steep and even decline. The annotated spike represents a multistate outbreak in which over 1,500 people contracted typhoid from eating raw oysters. Investigations of outbreaks like this, repeatedly implicated particular foods as vehicles of typhoid transmission. Raw oysters harvested from sewage contaminated waters, unpasteurized milk contaminated by asymptomatically infected milkmaids, and fresh vegetables fertilized with fresh night soil were most often implicated.

Three activities in the 1920's, 30's, and 40's brought the foodborne period of typhoid transmission to an end: legal reforms related to shellfish sanitation, pasteurization, and farming practices; tracking by public health personnel of asymptomatic typhoid carriers who were prohibited from working as food handlers; and the introduction of effective antimicrobial therapy.

Any thoughts on why the incidence of typhoid fever in the US has increased since the mid 1950s?