Kangra valley pilot project - the pioneer of National Iodine Deficiency Disorder Control Programme in India

In order to find out whether iodine deficiency is a causative factor of endemic goiter in the Himalayan belt and to find out the effectiveness of iodine prophylaxis, a prospective study was organized in 1956 in Kangra valley of Himachal Pradesh in India. (Sooch and Ramalingaswami, 1965). The study region was divided into A,B and C zones. After a baseline survey in 1956, the salt distributed to zones A and C was fortified with potassium iodide and potassium iodate, respectively, while zone B was supplied with unfortified salt. The salt fortification was at a level that supplied approximately 200 microgram of iodine per person per day. After six years of iodization, in 1962, a marked decrease in the prevalence of goiter was observed in zone A (from 38% to 19%) and zone C (38% to 15%) without any significant change in zone B. Six years later, in 1968, a systematic survey of goiter prevalence showed a further reduction in zones A and C (8.5% and 9.1% respectively). This project laid the foundation of National Goiter control project which later on was changed to National Iodine deficiency disorder control programme in India.

Secondary attack rate and Basic reproductive rate; what is the difference?

Secondary attack rate (SAR) is the proportion of susceptibles infected by getting exposed by one diseased individual in one incubation period. 

Basic reproductive rate; whereas is the potential for a contagious disease to spread from person to person in a population (in which all are susceptible). The basic reproduction rate (BRR) takes into account the population dynamics as we can know by this formula:
BRR= a x b x d
where; a is the risk of transmission per contact; b is the number of such contacts that an average person in the population would normally have per time unit and d is the duration of infectivity of an infected person, measured in the same time unit as b was. 

We find that the formula is very trivial (which i hv tried to keep for explaining the basic concept) and tells us that if the risk of transmission per contact is high, the number of contacts is also high among the people
in a population and the duration of infectivity of the diseased person is high then the BRR or the potential for a contagious disease to spread in a population will by high.

These all things are not taken into account by the Secondary attack rate which is very much representative of a fixed (static) model estimate whereas BRR is representative of a dynamic model estimate.