GIÁO TRÌNH DỊCH TỄ HỌC 2020 ĐHYD CẦN THƠ

TRUONG DAI HOC Y DUOC CAN THO KHOA Y TE CONG CONG - DICHTEHOC • • (Tal li~u Dung Bao Tao Chuyen Khoa clip I YTCC Nguoi Bien Soan PGS TS PRAM THl TAM C!NH NGHIA CUA D!CH T~ HQC Dich t~ h9C duoc dinh nghla nhu sau "dich tl h9C fa mot man h9C vi su phdn b6, va nhiing yiu t6 xac dinh cua nhiing bien quan din sire khoe trang nhiing ddn s6 C1:lthi, c6 va tinh trang lien va su ung dung man h9C trang viec kiim sa at nhiing vein di sire khoe " Khi mo ta v~ benh, hoac n6i chung la nhtrng hien tuong sire khoe, nha dich t~ h9C khong chi dien ta mot each chung chung rang benh da xay nhieu hay it mot t~p th~ nguoi, ma Cl,lth~ hon, ho se cho thay nhtrng t~n s6 va ti l~ benh (y nhtrng nh6m ngiroi c6 nhtrng thuoc tinh dac biet, cir ngu tai mot khu VlJCrieng biet, va van mot thai diem nao nam N6i mQt each khac, dich t~ h9C da cho chung ta thay ducc su ph an b6 cua benh theo tung nguoi (ai mac benh), khong gian (benh xay (y dau), va thai gian (benh xay nao) cu th~ Vi du, Trung tam kiim soat va phong ngua dich benh Trung Quoc gdn ddy all xudt ban loat cac truong h9'P voi s6 luong Ion nhdt cho ain hit 11 thang nam 2020 benh coronavirus 2019 (COVID-19) Trung Quoc dai luc la 72314 truong hop Trong ao, 44672 (62%) truong h9'P duac xac nhdn ch6n dodn dua tren kit qua xet nghiem axit nucleic duong tinh tren rndu benh phdm hong; 16186 (22%) truong h9'P nghi ngo; 10567 (15%) tnorng h9P duac ch6n doan va 889 (1%) truong h9'P kh6ng co trieu chimg Ph an b6 tudi (n =44672)cho thdy lua tudi mitc nhi~u nhdt la 30-79 tuoi: 87% (38 680 truong h9P)Va 20-29 tuo): 8% (3619 truong h9P); 3% (1408 truong h9P) ?.80 tudi va 2% (965 truong h9P) :: 19 tudi Thi b¢nh (n=44415), nhe la 81% (36160 a G:\GD CK2 DTH (mon ho tro CK2 QL YT)\DTH CK2 QL YT (Chuan hoa 2020 BV Quan TPHCM).docby PTT - - truong h9P), ruing 14% (6168 truong h9P) va nguy kich fa 5% (2087 truong hopj.Ti sudt tll: vong chung fa 2,3% (1023 s6 44672 truong hop duac xac nhdn); 14,8% o· benn nhdn ?: 80tu6i (208 tren 1408; 8,0% 6' benh nhdn he 70-79 tu6i (312 tren 3918) va 49,0% cac truong hop nguy kich (1023 tren 2087) Nhdn vien y ti bi nhiim benn fa 3,8% (1716 cua 44672) va 63% tai Vii han (1080 tren 1716) s6 truong hap phdt hien m6i the a bi6u hien lam sang va s6 truang hop xac nhdn duac trinh bay bidu a6 each mo ta benh COVID-19 thi du tren cho th~y SlJ xuat hien a nhtrng Ilia tu6i khac nhau, the benh khac nhau, nguy co nr vong cua benh khac theo the benh va thee tuoi, su xu~t hien benh nhan vien y t€ thay d6i thee khu VlJC - - - ~- • .• I ~ I rl - II -~ t - II I Wl-IO c'>el:i.ll~ "II¢lWtc 1~;I1d,~1I"1I9tocy lif jlltt",al~ ~C nguy cc, co mot loai don vi dac biet goi la thai gian-nguoi diroc dung cho m~u sf> cua cong thirc tinh ti suat moi mac Thi du, mot nghien ciru keo dai 10 nam d€ tinh s6 rnoi mac cua benh loet da day, neu ba benh nhan IAn hrot duoc then doi 3, 8, 10 nam, ho se dong gap 21 nam-nguoi van m~u s6 cua ti su~t moi mac Dan vi 'thai gian-nguoi J diroc dung tinh mot s6 moi mac khac goi la ti moi mac, TI su§t mrri m~c trung binh thuong duoc goi la ti moi hay s6 moi mac mac thai gian-nguoi hay Ti su§t, la s6 nlnrng ca benh moi khoi phat mot thai khoang thai gian nguy ca bang t6ng thai gian quan sat cua tung ca nhan dan s6, diroc tinh la nam-nguoi, thangnguoi, V.v Uu diem cua ti suat so voi nguy co' la no co tinh d~n nhtrng thai khoang quan sat ca nhan khac nhtrng ca nhan di van dan s6 nhirng thai diem khac nhau, hoac ho khong dan s6 vi nhtrng 1y khac (phat benh, chet, di chuyen, rut 1ui, v.v.) Ti su§t thuong ducc dung nhtrng nghien ciru doan h~ then d5i nhtmg benh co thai gian u benh keo dai, thi du nhtrng benh lien quan d~n nghe nghiep, AIDS, va nhfmg benh man tinh Ti su§t co nhtrng diem bat loi rieng cua no + Thir nhat, ti su~t bao gorn chung nhtrng khoang thai gian theo d5i khac MQt sf> it nguoi duoc theo doi lau dai (thi du theo d5i ngiroi vong nam), va mot s6 nhieu nguoi duoc then d5i ngan han (thi du theo doi 20 nguoi vong 0,5 nam) cfing se dong gap nhu vao m~u s6 thai gian-nguoi N~u nhtrng benh nhan duoc theo d5i ngan han co nhtrng thuoc tinh khac voi nhtrng thuoc tinh cua nhtrng benh nhan duoc then d5i lau dai, k~t qua cua ti su~t se bi sai lech G:\GD CK2 CHUAN HOA DTH va PC BTN\NDN-DTH-tailieu hoc tap BI-2-3 (Chuan hoa2020 BV Q2).doc - 12- + Thir nhi, kha nang mac benh hoac chet cua nhfrng ca nhan mot dan s6 thirong khong the hang dinh su6t thai gian ma chung ta thee d5i dan s6 Thi du, voi mot benh c6 thai gian tiem An dai thi ti suAt se thap khoang d~u thai gian thee doi, va se cao khoang cuoi cua thai gian thee d5i De giam sai lech, chung ta c6 the phan tich du kien thee tung thai khoang cua ca thai gian quan sat + Thir ba, voi nhtrng benh ur vong nhanh, ti suAt duoc se cao gia tao Vi mot tnrong hop ill vong nhanh se g6p mot don vi van ill s6, nhung se gop it hon mot don vi thai gian-nguoi van m~u s6 MBi Lien Quan Gifra SB Mo'i M~c vs SB Hi~n M~c S6 hien mac cua mot benh thuoc van y8u t6: c6 bao nhieu nguoi bi benh qua khir (tire la s6 moi mac truce day), va thai gian benh, M6i lien quan giira s6 moi mac voi s6 hien mac va thai gian benh duoc the hien bang cong thirc P ~ I x d, P la s6 hien mac (Prevalence), I la s6 moi mac (Incidence), va d la thai gian benh Cau hoi on t~p bai 2: Trinh bay s6 hien mac va s6 moi mac: Dinh nghia, cong thirc tinh, y nghia va m6i lien quan giua s6 hien mac va s6 moi mac C:\Users\V AIO SR56GG\Desktop\NDN summary of basis of Epidemiolgy.doc.doc - 11 - Bili s6 Do Ml}C K~t HQ'p vs s6 Do Tac DQng tieu bai glang Sau hoc xong bed nay, h9C vien Tinh toan duoc nhiing s6 co thd kit hop, g6m nguy co tuong a6i, tl s6 s6 chenh, nguy co qui trdch, va nguy co qui trach ddn s6 Ly giai duoc y nghia cua nhiing s6 noi tren ad xac dinh duac mot nguyen nhdn gay benh, va luong gia duoc tac a9ng cua nguyen nhdn a6i WYitinh trang stcc khoe cua mot cong a6ng Be mo ta sir xu§t hien cua mot hien tUQTIgsire khoe, chung ta sir dung nhtrng s6 benh trang hoac tir vong, la s6 hien mac va s6 rnoi mac, Hai s6 giup chung ta mo ta diroc hien trang cua benh, hoac kha nang mac benh tung dan s6 mot, Be xac dinh ducc nguyen nhan gay benh, chung ta can so sanh benh trang cua hai hoac nhieu dan s6 khac Chi nao dan s6 A, mac benh nhieu hon dan s6 B, mang nhtrng thuoc tinh khac voi dan s6 B, thi nhtrng thuoc tinh chi c6 a A ma khong c6 a B moi c6 the la nhirng nguyen nhan gay benh cho dan s6 A Be xac dinh duoc nguyen nhan gay benh, chung ta se sir dung nhtrng s6 ket hop, chung duoc goi la s6 lien quan, hay s6 hau qua Nhtrng s6 duoc tinh toan can cu vao su so sanh nhtrng s6 benh trang a nhtrng dan s6 mang nhtrng thuoc tinh khac Be so sanh hai s6 benh trang, hay n6i mot each khac, de xac dinh duoc s6 benh trang nao la Ian hon, chung ta c6 the chia hai s6 voi nhau, hoac tnr chung cho C:\Users\V AIO SR56GG\Desktop\NDN summary of basis of Epidemiolgy.doc.doc - 12 - -~ M{>tsa ta phoi nhi~m - Khai Ni~m: Nguyen nhan - Y~u Sl}' ta nguy co' - Nguy co - Y~u phrri nhi~m - Bang 2x2 Nguyen nhan gay benh hi m9t y€u t6, thong qua mot qua trinh voi nhtrng co che cu th~, c6 th~ gay mot benh 1;' dac thu Mycobacterium tuberculosis la nguyen nhan gay benh Lao ta Y~u a mot nguoi a nguoi nguy co': Y€u t6 nguy co cua benh la nhtrng y€u t6 hien dien cua n6 se tang kha nang mac benh Vi du moi tnrong a nhiern, bi suy dinh du5ng va khong chung ngira la nhtrng yeu t6 nguy co cua benh Lao Nguy co: Nguy co mac benh la xac suat xay benh, duoc th~ hien bang mot ti l~ y~u ta pho'i nhiem: nguyen nhan hoac yeu t6 nguy co duoc goi la y€u t6 phoi nhiem St}' phrri nhi~m: S1Jtiep xuc voi nguyen nhan hoac yeu t6 nguy co n6 duoc goi la S1Jphoi nhiem Bang 2x2: Bang 2x2 th~ hien moi lien quan giira hai bien s6, c6 th~ cho thay diroc S1Jthay d6i cua mot bien s6 theo S1Jthay d6i cua bien s6 lai Bang 2x2 duoc Slr dung ph6 bien dich t~ hoc phan tich d~ xac dinh nguyen nhan hoac nhtrng y€u t6 nguy co cua benh, D~ d~ tinh toan va 1;' giai nhtrng s6 c§n thiet, nen trinh bay du kien bang 2x2 theo thir t1J, nguyen nhan a hang, benh a C9t, va c6 truce, khong sau cfiu true t6ng quat cua bang 2x2 nhu sau: B~nh Yeu to nguy co C6 Khong Tong C6 a b a+b Khong c d c+d a+c b+d Tong a+b+c+d C:\Users\V ATO SR56GG\Desktop\NDN summary ofbasisofEpidemiolgy.doc.doc - 13 - Trang a la s6 nguoi co phoi nhi€m (co tiep xuc voi y€u t6 nguy co ) va co benh; b la s6 ngiroi co phoi nhiern nhung khong benh; c la s6 nguoi khong phoi nhiem nhung co benh; va d la s6 ngiroi khong phoi nhiem va cling khong benh Cac sa Do K~t HQ'p 2.1 Nguy coo turrng aai Nguy co tuong d6i duoc vi€t t~t la RR, nr thuat ngfr tieng Anh la relative risk hoac risk ratio Dua vao bang 2x2, chung ta co th~ xac dinh cong thirc d~ tinh RR nhir sau: Nguy co m~c benh nhom co phoi nhiem la R, = a / (a + b) Nguy co rnac benh nhom khong phoi nhiem la Ro = c / (c + d) V~y cong thirc d~ tinh nguy co tuong d6i, dua vao s6 moi mac la nguy co, la: RJ a/(a+b) Ro c/(c+d) RR= RR duoc tinh dira vao s6 moi mac, co th~ la nguy co, hoac ti suat N€u s6 moi mac la ti suat, RR la ti s6 ti suftt (s6 moi mac ducc ghi nhan theo khoang thai gian theo d5i khac tren tung d6i nrong khac voi don vi la thai gian-nguoi), va cling la nguy cO'tuong d6i Bang 2x2 d~ trinh bay nhtrng dfr kien cua s6 moi mac la ti suftt co cftu true nhu bang diroi day, a la s6 ngiroi co phoi nhiem va m~c benh tong thai gian theo doi la TGN1; va b la s6 nguoi kh6ng phoi nhiern va rnac benh tong thai gian theo d5i la TGNo C:\Users\YAIO SR56GG\Desktop\NDN summary of basis ofEpidemiolgy.doc.doc - 14- Bang 2x2 trinh bay dtr kien rnac benh voi s6 la ti su~t B~nh Y~u t6 nguy co C6 Khong Thai gian-nguoi C6 a - TGNI Khong b - TGNo T6ng TGN1+TGNo a+b V~y cong thirc d€ tinh RR dua vao s6 moi mac la ti suat, la: a ITGNj RR= b 1TGNo 2.2 Ti sa sa chenh MQt loai s6 benh trang khac, ngoai s6 hien mac va s6 moi mac, la s6 chenh, va diroc ky hieu la O S6 chenh duoc tinh theo cong thirc sau: Nguy co S6 chenh = - Nguy co N~u s6 chenh bang 0, thi nguy co bang 0, hay khong c6 nguy co mac benh N~u s6 chenh bang 1, thi nguy co bang 0,5 N~u s6 chenh bang 00, thi nguy co bang Nhir vay, s6 chenh c6 th€ hrong duoc nguy co m~c benh cua mot nguoi, va tl s6 cua s6 chenh c6 th€ duoc dung d€ so sanh kha nang mac benh cua hai ngiroi Cong thirc d€ tinh OR la: ad OR = be C:\Users\V AIO SRS6GG\Desktop\NDN summary of basis ofEpidemiolgy.doc.doc -.L ~~~ - IS- ~========~~_ Trong cong thtrc tinh RR, chung ta thay rang neu benh la hiem, a se nho, va (a + b) tirong duong b; tuong tv, c se nho, va (c + d) tirong duong d Khi do: aJ (a + b) RR = c/(c+d) a/b ~ - a == c/d d - x b c ad == == OR be Nhir vay, loai benh duoc khao sat la hiem, OR la s6 iroc hrong g~n dung cho RR 2.3 Y nghia cua sB k~t hop Nguy co nrong d6i va ti s6 s6 chenh duoc tinh theo nhtrng cong thirc khac nhau, nhung c6 cong dung va y nghia giong Chung giup cho chung ta hrong ducc mire d9 k~t hop giira nguyen nhan va benh Mire d9 k~t hop nhan qua duoc th€ hien qua gia tri bang s6 cua RR hoac OR N~u RR (hoac OR) bang 1, c6 nghia la nguy co mac benh a nh6m c6 phoi nhiem va nh6m khong phoi nhiem la bang nhau, hay n6i mot each khac, y~u t6 phoi nhiem khong c6 lien quan gi d~n benh, hay n6i mot each khac ntra, n6 khong la nguyen nhan gay benh Do do, RR va OR ducc goi la s6 lien quan N~u RR (hoac OR) c6 tri s6 khac 1, thi nguy co mac benh phoi nhiem la khac voi nguy ca mac benh a nh6m a nh6m khong phoi nhiern N~u RR (hoac OR) c6 tri s6 nho hon 1, thi nguy co mac benh cua nhtrng ngiroi c6 phoi nhiern la thap hon so voi nhtrng nguoi khong phoi nhiern Nguy co tuong d6i, RR, duoc tinh toan dua tren s6 benh trang la s6 moi mac (nguy co hoac ti suat), va duoc S11 dung nhfrng nghien ciru doan h~ Nghien ciru benh-clnmg khong th€ luong duoc mot each true tiep nguy cc mac benh, nhung tnrong hop loai benh ma chung ta khao sat la hiern, thi ti s6 s6 chenh OR c6 tri s6 g~n bang RR, tire la chung ta c6 th€ S11 dung OR d€ hrong nguy cc mac benh tuong d6i cua ngiroi c6 phoi nhiern so voi nguoi khong phoi nhiem C:\Users\Y AIO SR56GG\Desktop\NDN summary of basis of Epidemiolgy.doc.doc - 16 - 3.S6 Do Tac D