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Revista da Sociedade Brasi leira de Medicina Tropical 38( 2) :196-1 98 , mar-abr, 2005

Co mpariso n o f the thick sm ear and Kato -Katz techniqu es

fo r diagnos is o f intes tinal helm inth infectio ns

Com par ação das técnicas de sedime ntação e spon tânea e Kato-Katzpar a diagnó stico das helm intoses intestinais

Fred Luciano Neves Santos1, Elúzio José Lima Cerqueira1 and Neci Matos Soares1

ABSTRACT

This study compared the eff iciency of Kato-Katz thick smear and thick smear techniques for the diagnosis of i ntesti nal 

helmi nths. The sensiti vity of the thick smear technique was higher than that of the Kato-Katz method for the diagnosis of all helmi nths except Sc h i s to s o m a m a n s o n i.

Key-words : Kato-Katz. Direct examinati on. Sensit ivity. Specifi city. Prevalence.

RESUMO

O objeti vo deste trabalho foi comparar a efi ciência dos métodos de Kato-Katz e sedimentação espontânea para o 

diagnóstico das helmintíases intestinai s. A sensibi lidade da técni ca de sedimentação espontânea foi superi or aquela encontrada pelo método de Kato-Katz para o diagnóstico de todos os helmintos, exceto para Sc h i s to s o m a m a n s o n i .

Pal avras-chaves:  Kato-Katz. Sedimentação espontânea. Sensibi lidade. Especificidade. Prevalênci a.

1 . L a b o r a t ó r i o d e P a r a s i t o lo g i a C lí n i c a d a F a c u l d a d e d e F a r m á c i a d a U n i v e r s i d a d e F e d e r a l d a B a h i a , S a lv a d o r , B A.

T h i s w o r k w a s s u p p o r t e d b y t h e F u n d a ç ã o d e A p o i o a P e s q u i s a d o E s t a d o d a B a h i a ( FAP E SB ) . B r a z i l .

Address to: Dr . Fre d L uc i a no Ne ve s Sa n t os . L a b . de Pa ra s i t o l og i a C l í n i c a / FF/ UFBA. Av . Ba rã o de Ge re m oa bo , s / n . 41170-280 Sa l va dor , BA.

F a x: 5 5 7 1 2 3 7 - 2 2 5 5 .e - m a i l : n e c i @ u f b a . b r

R e c e b id o p a r a p u b l i ca ç ã o e m 2 8 / 1 0 / 2 0 0 3

A c e i t o e m 1 5 / 1 2 / 2 0 0 5

COMUNICAÇÃO/COMMUNICATION

I n 1 9 5 4 , K a t o a n d M i u r a i n t r o d u c e d a t h i c k - s m e a r

technique for feca l examina t ion 3 . Soon ther eafter, Katz mo dif ied

a n d a d a p t e d t h i s t e c h n i q u e f o r u s e i n f i e l d s t u d i e s 4 . This

m e t h o d w a s a d o p t e d  by WHO 8  fo r q ua nt i ta t ive and q ua l i ta t ive

d ia g n o s i s o f in t e s t in a l in f e c t io n s c a u s e d b y h e lmin th s s u c h

a s Ascari s lumbri coides , Trichuri s tri chiura , h o o k w o r m a n d

Schistosoma mansoni , and has a lso been used in labora tory

diagnos is8. Although the Kato-Katz metho d is wide ly used for the

d i a g n o s i s o f i n t e s t i n a l h e l m i n t h s i n f e c t i o n s , i t s r e p o r t e d

effectiveness varies. Garcia et al2  observed that the Kato-Katz

method was mor e sens i t ive than the th ick sm ear technique for

d iagnos ing he lminths 2, while Martin & Beaver 5   conc luded tha t

the Kato th ick-smear technique is r e l iab le and prac t ica l for the

quan t ita tive d iagnos is of hoo kworm , Tri churi s Tri chiura   an d

Schistosome  infections5 . On the o ther hand , Enge ls e t a l1  showed

that the Kato-Katz method is no t suitable for h ook worm , pro tozoa

and f ilar iform larvae detection 1; while ano ther s tudy conc luded

th a t th e Ka to me th o d h a s a lo w s e n s i t iv i ty f o r id e n t i f y in g

hookworm eggs , and observed tha t hookworm eggs co l lapsed

and d isappeared shor t ly a fte r the th ick smear had c leared 9 . Here ,

we pr esent a co m par ative study of the Kato-Katz and thick sm ear

methods for de tec t ion of Ascaris lumbricoides, T. trichiura ,

h o o k wo r m a n d S. mansoni .

This s tudy was based on 258 stool samples collected from

schoo l-children , aged 6-14 years, from Salinas da Margarida County

Public School ( Bahia State), from January to June 200 1. All samples

were examined by the quantitative Kato-Katz and the qualitative

th ic k s me a r me th o d s , a c c o r d in g to s t a n d a r d iz e d p r o c e d u r e s

described elsewhere 6. Three slides were pre pared p er person , and

egg-coun ts from Kato-Katz slides were cond ucted 24 hour s af ter

its preparation. The sensitivity and specificity of each method in

isolation and of the two methods together were calculated using

Epi- info (version 6) software. The kappa statis tic 15 was used to

assess the concordance of tes t r esu l ts ob ta ined with the two

individual techniques, and McNem ar’s test for paired prop ortions

was used to compare the prevalences obtained with each of the

individual metho ds, accord ing to the no rm al theory test7.

O v e r a l l , 8 9 . 1 % o f s a m p l e s w e r e p o s i t i v e f o r c y s t s o f  

p r o t o z o a ( d a t a n o t s h o w n ) a n d / o r h e l m i n t h e gg s ( Ta b l e 1 ) .

Th ic k s m e a r id e n t i fi e d a l a r g e r f r a c t io n o f p a t i e n t s in fe c te d

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Santos FLN et al 

w i t h h e l m i n t h s . T h e d i f f e r e n c e w a s m o s t e v i d e n t f o r

h o o k wo r m, wh e r e th e r a t io o f p o s i t ive s a mp le s id e n t i fi e d b y

t h i c k s m e a r a n d K a t o - K a t z w a s 7 3 : 1 . H o w e v e r , c o m b i n e d

exam ination with the thick sme ar an d Kato-Katz techn iques gave

better results than when the thick-smear was used alone (Table 1).

Com par ed to thick sm ear, the sen sitivity of the Kato-Katz metho d

was 68 .2% for T. tri chiura , 70 .8% for A. lumbricoidesand 1 .4%for hoo kworm , and the spec ific ity was 60 .2 % for T. tr ichiura ,

84 .1% for A. lumbri coides , and 100% for hookworm ( Table 2) .

However, the infection s detected with these d iffere nt techn iques

we r e n o t n e c e s s a r i ly th e s a me , wh ic h me a n s th a t e v e n th e

sensitivity of these improved   individual techniques is far f rom

idea l , and hea l th per son ne l should be aware tha t a per son is no t

to be classif ied as uninfected on the basis of a s imple negative

examina t ion by one of these techniques cond uc ted in iso la t ion .

The Kappa statistic indicated that agreem ent between the Kato an d

thick sm ear m ethods was good for A. lumbricoides (κ  = 0 .5 5 ) ,

a n d m a r g i n a l f o r T. tri chiura   ( κ  = 0 . 2 7 ) a n d h o o k w o r m

( κ  = 0.02) . In addition, McNem ar’s test indicated that direct

examination was more likely to correctly identify T. trichiura  than the

Kato-Katz method (χ2 = 3.64, p = 0.056), although the prevalences of 

A. lumbricoides were not significantly different (χ2 = 2 .526 , p = 0 .11) .

However , compar ison of the ind iv idua l methods with theMcNema r test indicated that direct exam ination was m ore r eliable

for determ ining infection with T. tr ichiura . Larger sample sizes

would be nec essary for deter mining whether the direc t examina tion

is also mo re r eliable for detecting A. lumbricoides .

The pre sent s tudy fou nd th at the Kato-Katz metho d wer e less

sens i tive than th ick smear for de tec t ing hoo kworm infec t ions .

P r e v io u s r e p o r t s 1 9   have sugges ted tha t Kato-Katz could beadequ a te for de tec t ing hoo kworm . However , these s tud ies only

exam ined a s ingle s lide p er p atient, and th e Kato-Katz slides were

read imm edia te ly a fte r pr epara t ion . I t is l ike ly tha t ho okworm

eggs de te r iora te dur ing the s tandard ized 24-hou r per iod before

slide readin g, which would explain the low p revalences identifiedby Kato-Katz in this s tu dy. Neverthe less, we con clude d th at the

Kato-Katz method, when used with the thick smear, would be

Table 2 -Resul ts of t hick smear and Kato-Katz anal ysi s of 258 stool samples fr om publ i c school chi l dren i n Sali nas da 

Margari da County, Bahia.

  Thick smear

Kato -Katz positive negative sensitivity sp ecific ity Kappa In dex

( %) ( CI) ( %) ( CI) ( CI)

T. tri chiura  po sitive 116 35 6 8 .2 6 0 .2 0 .27

( 61 .2 – 75 .2 ) ( 50 .0 – 70 .5 ) ( 0 .15 – 0 .39 )

negative 54 53

A. lumbricoides  po sitive 85 22 7 0 .8 8 4 .1 0 .55

( 62 .7 – 79 .0 ) ( 78 .0 – 90 .2 ) ( 0 .45 – 0 .66 )

negative 35 116

Hookworm  po sitive 1 0 1 .4 1 00 0 .0 2

( -.1 .3 – 4 .0 ) - ( -0 .17 – 0 .21 )

Negative 72 185

S. mansoni  po sitive 1 1 1 00 9 9 .6 0 .6 6

- ( 98 .8 – 10 0 .4 ) ( 0 .01 – 1 .32 )

negative 0 256

Table 1 - Prevalence of common i ntesti nal parasi tes detected by dif ferent 

techni ques of faeccal examinat ion in 258 chil dren from a publ i c school 

i n Sal inas da Margari da, Count y, Bahia.

  Prevalence ( %)

Par asite Th ick sm ear Kato -Katz Th ick sm ear +

Meth od techn ique Kato -Katz techn iq ues

Helminthes,

Eggs/larvae

T. tri chiura  1 70 ( 66 .0%) 13 1 ( 58 .5 %) 205 ( 79 .5 %)

A. lumbricoides  1 20 ( 46 .5%) 10 7 ( 41 .5 %) 142 ( 55 .0 %)

Hookworms  73 ( 2 8 .3%) 1 ( 0 .4 %) 7 3 ( 28 .3 %)

S. stercorali s  4 ( 1 .5%) - 4 ( 1 .5 %)

E. vermiculares  3 ( 1 .2%) - 3 ( 1 .2 %)

S. mansoni  1 ( 0 .4%) 2 ( 0 .8 %) 2 ( 0 .8 %)

particular ly appropriate for large-scale surveys because of its

simp licity, lower cost, an d r apidity.

ACKNOWLEDGEMENTS

To Craig Andr ews Milroy for his h elp with the cr itical review

of the manuscript and for s tatis tical analysis .

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