Revista da So ciedade Brasileira de M edicina Tropical 2 9 (6 ):6 l9 - 6 2 0 , nov - dez, 1996.
CA RTA A O ED ITO R
IN TRA D ERM IC SU RV EY W IT H H ISTO PLA SM IN A N D
PA RA CO CCID IO ID IN
Sir,
T h e sp ecificity o f skin tests u sing th e Fav a- N e tto h is to p la s m in an d p a ra c o c c id io id in antig ens has b e e n q u estio n ed b e fo re 1. In a re c en t su rv ey in Rio G rand e d o Sul (RS) 3 an ap p arent e x c e ss o f d o u b le-p o sitiv e results w as ag ain tak e n to su g g est cro ss-reactio n. If these antig ens w ere to b e sh o w n to b e u nsp ec ific they w o u ld b e u sele ss fo r ep id em io lo g ical su rv ey s, and th e c red ib ility o f th e m any su rv ey s in w h ic h they hav e b e e n u sed w o u ld b e serio u sly u nd erm ined .
Fo rtu nately , the co rrelatio n o f p o sitiv e tests c an b e ex p lain e d b y o th e r facto rs, inclu d ing ex p erim en tal d esig n. If H O is th e nu m b er o f ind iv id u als p o sitiv e o nly to histo p lasm in, PO o n ly to p arac o c c id io id in , HP to b o th and O O to n e i t h e r , t h e n t h e R S d a t a3 c a n b e su m m ariz ed as fo lo w s:
H O PO HP O O
49 19 199 85 o b serv ed
93 65 155 39 exp ec ted -44 -46 +44 + 46 d ifference
H o w ev er, this is n o t p erm issib le, b ec au se tw o sam p les w ith d ifferent characteristics, C acho eira d o Sul (C S) and Santo A ng elo (SA ) w ere p o o le d . T h e e x p e c te d nu m b er o f HP resu lts if H and P are in d ep ed en t is in fact 170.5, w hic h is c lo se r to the o b serv ed
value.-HO PO HP O O
CS N= 191 30 17 140 4
SA N= l6l 47.5 32.5 30.5 50.5
To tal 77.5 49.5 170.5 54.5
O b serv ed 49 19 199 85
D ifferenc e -28.5 -30.5 +28.5 +30.5
C o o rd en ad o ria d e Pesq uisas da Saúde d o In stitu to N acional d e Pesq uisas d a A m azônia, M anaus, A M .
Endereço para co rrespo ndência: D r. T o b y V in cen t Barrett. IN PA /CPCS. C P 4 7 8 ,6 9 0 1 1 - 9 7 0 M anaus,A M , Brasil R eceb id o p ara p u b licação em 1 9 / 0 6 / 9 6 .
In a su rv ey2 u sing th ese antig ens in the To cantins b asin, th e freq u en c y d istrib u itio n o f ind u ratio n d iam eter su g g ested that reactio ns o v er 3.0m m w ere p o sitiv e, and that ad o p ting a thresho ld o f 5.0m m resu lted in ab o u t 6% false n eg etiv e results fo r histo p lasm in and 7% false neg ativ e results fo r p araco ccid io id in. Increasing th e sensitiv ity o f th e test b y sc o ring sm aller ind u ratio ns as p o sitiv e w o u ld p ro b ab ly alter the co rrelatio ns (5.0m m w as u sed in RS).
If th ese antig ens are no t sp ec ific , h o w d o es o n e ex p lain the 68 su b jec ts w ho reac ted to o nly o n e antig en? C o rrelatio n o f reactiv ity to sp ec ific antig ens m ay ind icate a c o m m o n o r c o r r e la te d r i s k - f a c to r f o r e x p o s u r e to th e f u n g u s, o r b e d u e to f a ls e d o u b le - n e g a tiv e reactio ns cau sed b y the p re se n c e o f anerg ic ind iv id uals. Th e latter p o ssib ility c an b e tested fo r b y inclu d ing a third , u nrelated , antig en in th e surv ey , as w as d o n e in th e To cantins stud y 2.
A v ailab le re su lts in d ic a te th at th e Fav a- N e tto sk in - te s t a n tig e n s are s e n s itiv e an d sp ecific ind icato rs o f ex p o su re to the resp ectiv e fung i, and that risk facto rs fo r ex p o su re are p o o rly c o rre la te d , at le a s t in th e A m az o n re g io n 2. If f u rth e r e v id e n c e o f s p e c if ity in asy m p to m atic ind iv id uals is req u ired , a su rv ey w ith th ese antig ens co u ld b e c o n d u c te d in an area w h ere H isto plasm a cap s ulat um is p resent and P araco ccidio ides brasiliens is ab se n t (eg N o rth A m erica), o r a u niv ersal an tig en co u ld b e u sed as a p o sitiv e c o n tro l, in a future stud y.
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To by V incent B arret t
