The first area to be involved in an outbreak of cholera El Tor in India was Calcutta where El Tor strains were indentified in April 1964. Another focus harboring this disease has recently come to light in the course of routine phage-typing of the causal strains isolated in cholera epidemics in Surat and Baroda in the State of Gujarat. The El Tor strains of Surat and Baroda were nonhemolytic and therefore indistinguishable by hemolytic test from the Vibrio cholerae strains isolated simultaneously. In the absence of phage-typing the V. el tor strains from Gujarat would have passed as classical cholera vibrios. The value of routine phage-typing of strains isolated in all fresh cholera outbreaks has thus been confirmed. By the use of chicken erythrocytes in place of sheep cells in the hemolysis test, all the apparently non-hemolytic V. el tor strains proved hemolytic. But the diagnostic value of the chicken-cell test is minimized because of the lysability of chicken erythrocytes by some classical cholera vibrios.
The V. el tor strains from Gujarat differed in phage-sensitivity patterns from those isolated in the Calcutta area. Phage-typing of El Tor strains from all the future cholera El Tor outbreaks in India is likely to provide valuable information about the mode of spread in India of cholera in general and cholera El Tor in particular.