Table 2 Results of the interviews and data collection related with the positive predictive value and representativeness attributes of the surveillance system

Positive predictive value

Positive predictive value during an inter-epidemic period

For the initial fifth through tenth suspected cholera cases, stool samples were collected to perform stool cultures. This was done in the national laboratory in Niamey. Stool collection usually lacked for the first cholera cases. Tubes with Cary-Blair medium for the transport of the samples were not available from 2006 to 2009. For 26 cholera cultures results from 2006 to 2009 available at the time of the study, 13 were positive for Vibrio cholerea O1 ogawa (2 were positive for shigella and no pathogens were found for 11 cultures).

Positive predictive value during an epidemic period

Each epidemic was confirmed by stool culture. If an epidemic was confirmed with five to ten stool samples, stool collection and testing ceased. Four heads of health structures reported that during an epidemic, the population was aware of the gravity of cholera and that they were more likely to seek care at healthcare facilities in case of acute diarrhea.

Representativeness

Accurate description of cholera cases over time

Each week, each healthcare facility completed the notifiable diseases reports, which include the number of cholera cases. When a cholera case is suspected, the head of the healthcare facility promptly contacted the district epidemiologist, who in turn contacted the regional responsible of the surveillance system. During an epidemic, the count of cholera cases was reported daily to the regional and national heads of the surveillance system.

Accurate description of cholera cases by geographic location

In remote villages, the first cholera cases did not seek care at healthcare facilities. After a few cases had been noted, the population tended to seek care at health facilities.

Accurate description of cholera cases by socio-demographics characteristics

For each cholera case, specific forms were completed with accurate information including: age, sex, address, consultation date, report date, date of symptom onset, vital status, and final diagnosis.Individuals aged less than 5 years are not typically reported. Some cases in children under 5 were reported, however.