Cyclic trend is shown by -

Ans, is 'c' i.e., Influenza pandemic Periodic fluctuationso Periodic fluctuation may be -Seasonal trendCyclic trendSeasonal trendo Some diseases show seasonal variations.o These changes are related to environmental conditions e.g., rainfall, overcrowding, humidity etc.o Examples are -i) Measlesii) Varicella (chicken pox)}- Early springiii) Upper respiratory' tract infection - Winteriv) GIT infection (including polio)v) Cerebrospinal meningitisvi) Rubella - late winter and springvii) Dengue - (in India)Cyclic trendo Some diseases occur in cyclic spread over a short period of time which may be week, days, months or years,o This is due to naturally occuring variation in herd immunity.o A build up of susceptible is again required in the herd before there can be another attack,o It may be due to antigenic variations as occur in influenza,o Examples - Epidemic ofi) Measlesii) Rubellaiii) Pandemic of influenza- every 2-3 years- every 6-9 years- every 10-15 yearsLong term or secular trendso The term secular trend implies changes in the occurrence of disease over a long period of time, generally several years or decades.o There may be progressive increase or decrease in the occurrence of disease,o Examples -CHD, lung cancer, and DM have shown a consistent upward trend in developed countries.TB, typhoid fever, diphtheria and polio have shown a declined trend in developed countries.