Floods can po­ten­tial­ly in­crease the trans­mis­sion of com­mu­ni­ca­ble wa­ter-borne dis­eases such as ty­phoid fever, cholera, lep­tospiro­sis and he­pati­tis A, and vec­tor-borne dis­eases, such as malar­ia, dengue and dengue haem­or­rhag­ic fever, yel­low fever, and West Nile fever.

Wa­ter-borne dis­eases

Flood­ing is as­so­ci­at­ed with an in­creased risk of in­fec­tion. How­ev­er this risk is low un­less there is sig­nif­i­cant pop­u­la­tion dis­place­ment and/or wa­ter sources are com­pro­mised. The ma­jor risk fac­tor for out­breaks as­so­ci­at­ed with flood­ing is the con­t­a­m­i­na­tion of drink­ing-wa­ter fa­cil­i­ties, and even when this hap­pens, the risk of out­breaks can be min­imised if the risk is well recog­nised and dis­as­ter-re­sponse ad­dress­es the pro­vi­sion of clean wa­ter as a pri­or­i­ty. The on­ly epi­dem­ic-prone in­fec­tion which can be trans­mit­ted di­rect­ly from con­t­a­m­i­nat­ed wa­ter is lep­tospiro­sis, a zoonot­ic bac­te­r­i­al dis­ease. Trans­mis­sion oc­curs through con­tact of the skin and mu­cous mem­branes with wa­ter, damp soil or veg­e­ta­tion (such as sug­ar­cane) or mud con­t­a­m­i­nat­ed with ro­dent urine. The oc­cur­rence of flood­ing af­ter heavy rain­fall fa­cil­i­tates the spread of the or­gan­ism due to the pro­lif­er­a­tion of ro­dents which shed large amounts of lep­tospires in their urine.

Vec­tor-borne dis­eases

Floods may in­di­rect­ly lead to an in­crease in vec­tor-borne dis­eases through the ex­pan­sion in the num­ber and range of vec­tor habi­tats. Stand­ing wa­ter caused by heavy rain­fall or over­flow of rivers can act as breed­ing sites for mos­qui­toes, and there­fore en­hance the po­ten­tial for ex­po­sure of the dis­as­ter-af­fect­ed pop­u­la­tion and emer­gency work­ers to in­fec­tions such as dengue, malar­ia and West Nile fever. Flood­ing may ini­tial­ly flush out mos­qui­to breed­ing, but it comes back when the wa­ters re­cede. The lag time is usu­al­ly around six to eight weeks be­fore the on­set of a malar­ia epi­dem­ic. The risk of out­breaks is great­ly in­creased by com­pli­cat­ing fac­tors, such as changes in hu­man be­hav­iour (in­creased ex­po­sure to mos­qui­toes while sleep­ing out­side, a tem­po­rary pause in dis­ease con­trol ac­tiv­i­ties, over­crowd­ing), or changes in the habi­tat which pro­mote mos­qui­to breed­ing (land­slide, de­for­esta­tion, riv­er damming, and rerout­ing).

Oth­er health risks posed by flood­ing

• These in­clude drown­ing and in­juries or trau­ma. Tetanus is not com­mon af­ter in­jury from flood­ing, and mass tetanus vac­ci­na­tion pro­grammes are not in­di­cat­ed. How­ev­er, tetanus boost­ers may be in­di­cat­ed for pre­vi­ous­ly vac­ci­nat­ed peo­ple who sus­tain open wounds or for oth­er in­jured peo­ple de­pend­ing on their tetanus im­mu­ni­sa­tion his­to­ry.

• Hy­pother­mia may al­so be a prob­lem, par­tic­u­lar­ly in chil­dren, if trapped in flood­wa­ters for lengthy pe­ri­ods. There may al­so be an in­creased risk of res­pi­ra­to­ry tract in­fec­tions due to ex­po­sure (loss of shel­ter, ex­po­sure to flood wa­ters and rain).

• Pow­er cuts re­lat­ed to floods may dis­rupt wa­ter treat­ment and sup­ply plants there­by in­creas­ing the risk of wa­ter-borne dis­eases as de­scribed above, but may al­so af­fect prop­er func­tion­ing of health fa­cil­i­ties.

Pre­ven­tive mea­sures

Com­mu­ni­ca­ble dis­ease risks from flood­ing can be great­ly re­duced if the fol­low­ing rec­om­men­da­tions are fol­lowed.

• Chlo­ri­na­tion of wa­ter: En­sur­ing un­in­ter­rupt­ed pro­vi­sion of safe drink­ing wa­ter is the most im­por­tant pre­ven­tive mea­sure to be im­ple­ment­ed fol­low­ing flood­ing, in or­der to re­duce the risk of out­breaks of wa­ter-borne dis­eases.

• Vac­ci­na­tion against he­pati­tis A: Vac­ci­na­tion of high-risk groups, such as peo­ple in­volved in the man­age­ment of drink­ing wa­ter, waste wa­ter or sewage might be con­sid­ered.

• Malar­ia pre­ven­tion: Flood­ing does not nec­es­sar­i­ly lead to an im­me­di­ate ma­jor in­crease in mos­qui­to num­bers, and there may still be time to im­ple­ment pre­ven­tive mea­sures such as in­door resid­ual spray­ing, or the re­treat­ment/dis­tri­b­u­tion of ITNs in ar­eas where their use is well-known. This will al­so have an ef­fect on oth­er mos­qui­to-borne dis­eases.

• Health ed­u­ca­tion: Pro­mote good hy­genic prac­tice. En­sure safe food prepa­ra­tion tech­niques. En­sure boil­ing or chlo­ri­na­tion of wa­ter. Vi­tal im­por­tance of ear­ly di­ag­no­sis and treat­ment for malar­ia (with­in 24 hours of on­set of fever). (WHO)