1973–1983 vs 1998–2008.doi:10.1371/journal.pntd.0001416.t003
Statistical analysis of temporal change in ciguatera incidence showed varied results. There was no statistically significant difference between 1973–1983 mean incidence and 1998–2008 mean incidence across PICTs (p = 0.949), comparing all PICTs (except the State of Hawaii which was not presented by Lewis ) using paired t-test (Table 4). However, there was a highly significant difference in mean incidence, between the two time periods when comparing mean incidence across years (p = 0.002), using independent-sample t-test. Linear regression analysis of annual mean incidence from 1973 to 2008 was also statistically significant (p = 0.005) despite high inter-year variability. The rate ratio (1998–2008 mean annual incidence/1973–1983 mean annual incidence) was 1.60; therefore, there was a 60% increase in the mean annual incidence from the earlier period to the more recent period. Hawaii, North Marianas, Marshall Islands, and Palau were omitted for the independent sample t-test, regression analysis and the rate ratio due to data limitations (Table 1).
Table 4. Change in the incidence of ciguatera: 1973–1983 vs 1998–2008.doi:10.1371/journal.pntd.0001416.t004
Of the 18 PICTs in this study, 11 reported on all (i.e. coral bleaching, cyclone incidence and perceived reef condition), whilst New Caledonia reported only on coral bleaching (Table 5). All three environmental disturbance types were positively related to ciguatera incidence. However, there was no statistically significant correlation between mean annual ciguatera incidence and occurrence of bleaching (p = 0.20), cyclone incidence (p = 0.17) or perceived coral reef condition (p = 0.57).
Table 5. Cyclones, coral bleaching and reef conditions reported by participating PICT: 1998–2008.doi:10.1371/journal.pntd.0001416.t005
Social consequences of ciguatera
Responses to questions relating to the social consequences of ciguatera demonstrated that the incidence of ciguatera might be having a negative impact on PICT communities. Seven PICTs reported changes in diet as a result of ciguatera, whilst six PICTs reported that there was no change in diet as a result of ciguatera. Also, seven PICTs reported secondary medical problems (such as diabetes due to dietary changes) as a result of ciguatera. Five PICTs reported both a change in diet and secondary medical problems as a result of ciguatera. Seven PICTs reported taking reactive management measures (such as closure of fishing areas) to manage ciguatera outbreaks, whilst four PICTs reported taking no reactionary measures. Four PICTs reported that preventative management (such as catchment management) was occurring, whilst four PICTs reported that there was no preventative management. Eight PICTs reported that additional support would improve the management of ciguatera, whilst four reported that it would not.
There was a positive and marginally significant relationship between changing diet and per capita incidence of ciguatera (p = 0.06), and secondary medical problems and per capita incidence of ciguatera (p = 0.08) (Table 6). Neither reactive nor proactive management was correlated with per capita incidence of ciguatera. However, perceived improvement in management as a result of increased support was positively correlated with per capita incidence of ciguatera (p = 0.013). There was no significant difference (p≤0.05) in per capita incidence of ciguatera between nations that did and did not respond to questions on the social consequences of ciguatera.
This study provides four important findings. First, as hypothesized, ciguatera incidence has increased significantly in the Pacific since the 1970s, but there is significant variability in incidence within PICTs since this time. Second, predicting causes of outbreaks and consequent elevated levels of ciguatera is difficult at the scale of this study, highlighting the need for further local-scale research and management action. Third, as reported earlier , ciguatera incidence continues to have significant negative effects on PI