Therapy of Experimentally Induced Rhinovirus Colds

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1 ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Aug. 1987, p /87/ $02.00/0 Copyright D 1987, Americn Society for Microbiology Vol. 31, No. 8 Two Rndomized Controlled Trils of Zinc Gluconte Lozenge Therpy of Experimentlly Induced Rhinovirus Colds BARRY M. FARR,'* EDWARD M. CONNER,2 ROBERT F. BETTS,3 JAMES OLESKE,2 ANTHONY MINNEFOR,2 AND JACK M. GWALTNEY, JR.' Deprtment of Internl Medicine, University of Virgini School of Medicine, Chrlottesville, Virgini ; Deprtment of Peditrics, New Jersey Medicl School, Newrk, New Jersey ; nd Deprtment of Internl Medicine, University of Rochester, Rochester, New York Received 9 Mrch 1987/Accepted 11 My 1987 The therpeutic efficcy of zinc gluconte lozenge therpy in experimentlly induced rhinovirus infection ws ssessed in two rndomized controlled trils in susceptible dult volunteers. In tril 1, lozenges contining either zinc gluconte (23 mg of elementl zinc) or plcebo were given 36 h fter nsl inocultion of rhinovirus type 39 nd dministered eight times per dy for 5 dys. All of the volunteers hd erly cold symptoms t the time tht tretment ws begun. In tril 2, the sme lozenge regimen ws used, beginning 2 h fter nsl inocultion with rhinovirus type 13, nd continued for 7 dys. Zinc therpy did not reduce the severity, or durtion of cold symptoms or the frequency or durtion of virl shedding in either tril. Virl titers were mesured in tril 2 nd were shown to be unffected by zinc therpy. Nsl mucus weights nd the numbers of pper tissues used were slightly higher in zinc recipients. A sttisticlly significnt increse in levels of zinc in serum ws documented in zinc recipients fter 5 dys of therpy. These dt suggest tht zinc gluconte lozenge therpy is not therpeuticlly useful in the tretment of rhinovirus colds. The common cold is one of the most frequent fflictions of mnkind nd the most frequent cuse for visits to physicins in the United Sttes. There is still no effective therpy for the mny viruses cusing this condition. Zinc hs been shown to inhibit virl polypeptide clevge, thus inhibiting the repliction of severl viruses which cuse common colds (1, 2, 9, 10), but the ntirhinovirl ctivity in WI-38 or HeL cell monolyers is only modest (5). A rndomized controlled tril of zinc gluconte lozenge therpy in nturlly cquired common colds hs suggested remrkble efficcy, with symptom durtion reduced by hlf (4). Blinding efficcy ws not ssessed in tht tril, however, nd higher dropout rte mong zinc recipients thn mong plcebo recipients suggests the possibility tht blinding ws ineffective. We hve developed tste-mtched plcebo contining dentonium benzote ( bitter substnce used to discourge thumb sucking in children) nd hve demonstrted in previous studies tht our zinc nd plcebo lozenges re comprble both in pltbility nd in the proportion of subjects who believe they re receiving ctive mediction (B. M. Frr nd J. M. Gwltney, Jr., J. Chronic Dis., in press). These mtched lozenges were used to conduct two plcebocontrolled double-blind trils to ssess the efficcy of zinc gluconte lozenge therpy in humn model of experimentlly induced rhinovirus infection. MATERIALS AND METHODS Subjects. Helthy dult volunteers (n = 32) with titers of serum neutrlizing ntibody to rhinovirus type 39 of <1:2 were ssigned by prior computer rndomiztion to receive either zinc gluconte or plcebo lozenge therpy in tril 1, nd 45 helthy dult volunteers with titers of ntibody to rhinovirus type 13 of.1:2 were enrolled in tril 2. Exclusion criteri included symptoms of ny respirtory illness in the week before the study, history of hyfever, ny fmilirity * Corresponding uthor with the tste of either dentonium benzote or zinc, history of ny chronic disese, pregnncy, lcttion or n uncceptble contrceptive method in women of childbering potentil, nd known buse of hbit-forming drugs. Volunteers gve informed consent for prticiption in this study fter being told tht one of the two study lozenges might be n effective therpy for colds. The protocol for tril 1 ws pproved by the Humn Investigtion Committee of the University of Virgini, nd for tril 2 the protocol ws pproved by the Institutionl Review Bord of Essex County, New Jersey. Lozenges. The lozenges were identicl in size, shpe, nd ppernce nd were similr in tste, s documented in our previous studies. Both lozenges contined 2% citric cid nd lemon flvoring. The zinc gluconte lozenge (RF 2546; Bristol Myers Products, Hillside, N.J.) contined 23 mg of elementl zinc. The plcebo lozenge for tril 1 (RF 2547; Bristol Myers Products) contined mg of dentonium benzote, nd the plcebo lozenge for tril 2 (RF 2548; Bristol Myers Products) contined mg of the sme compound. Ech lozenge ws wrpped in cellophne nd pckged in n opque polyethylene bottle bering the study number, the nuniber of the subject, the tretment dy, nd dosing instructions. Virl chllenge. Volunteers were dmitted to motel where they were housed in seprte rooms from the time of virl chllenge until 7 dys fterwrd. Rhinovirus type 39 ws dministered by intrnsl drops (0.25 ml per nostril) on two occsions 30 min prt just fter dmission to the motel in tril 1. The virl inoculum pool hd titer of % tissue culture infective doses per ml. A 1:10 (vol/vol) dilution of this pool ws used for inocultion. Rhinovirus type 13 ws similrly dministered by intrnsl drops (0.25 ml per nostril) from 1:5,000 (vol/vol) dilution of n inoculum pool with concentrtion of % tissue culture infective doses per ml in tril 2. Tretment pln. Ech subject ws observed by nurse when tking ech dose of test mediction. Subjects were

2 1184 FARR ET AL. ANTIMICROB. AGENTS CHEMOTHER. TABLE 1. Infection rtes nd virl shedding in rhinovirus type 39-inoculted volunteers Type of tretment No. of subjects No. No. with No. of virus- Durtion of shedding (dys)d (no. treted) shedding virus (%) seroconverting" (%) infection' (%) positive dys" (%) Men (tsem) Medin Zinc (16) 16 (100) 10 (63) 16 (100) 87 (90.6)e 6.9 (±0.3) 7 Plcebo (16) 14 (88) 9 (56) 15 (94) 66 (73.3)e 6.3 (±1.8) 7 Defined by fourfold or greter rise in serum-neutrlizing-ntibody titer. b Defined by shedding virus or fourfold or greter rise in serum-neutrlizing-ntibody titer. c Number of dys of observtion on which infected subjects shed virus. d Dys fter virl chllenge. Virl cultures were done on study dys 2 to 7. e Chi squre, 9.52; P < instructed not to chew or swllow the lozenges but to llow them to dissolve in the mouth nd to rise their hnds when only smll residuum remined so tht this could be verified nd documented on log sheet for ech dose in ech subject. Tretment ws begun on study dy 2 t 8.m., 36 h fter virl inocultion, in tril 1. In tril 2, tretment ws begun 2 h fter virl inocultion, which occurred t 7.m. on study dy 1. The first dose consisted of two lozenges, one followed by the other. Subsequent doses consisted of single lozenge, nd the dosge intervl ws 2 h. A totl of eight doses ws dministered ech dy for 5 dys in tril 1 nd for 7 dys in tril 2. The totl dily dosges of zinc were 207 mg on dy 1 of tretment nd 184 mg on ech subsequent study dy in tril 1 nd 184 mg ech dy in tril 2. Surveillnce nd smpling. Tril 1 subjects were interviewed in the fternoon before virl chllenge (study dy 0) nd then ech morning on study dys 1 through 7 regrding eight common cold symptoms, including sneezing, nsl dischrge, nsl congestion, mlise, hedche, chilliness, sore throt, nd cough. Subjects were interviewed ech morning nd fternoon in tril 2. Symptoms were rted for severity ccording to the following scle: 0, none; 1, mild; 2, moderte; nd 3, severe. Criteri for cold were bsed on modifiction (6) of the criteri proposed by Jckson et l. (8) nd required totl symptom score of.5 plus either nsl dischrge for 3 dys or the belief of the subject tht cold hd occurred. After dischrge from the motel, subjects kept dily record of the sme cold symptoms for 7 dys. Ech subject ws contcted twice by telephone during this period to ssure complince in keeping the diry. After the study prticipnts blew their noses, their pper tissues were collected nd stored in irtight continers. These tissues were collected dily, counted, nd weighed to determine nsl mucus weights. Clinicl lbortory tests, including complete blood count, differentil leukocyte count, metbolic profile, heptic enzymes, urinlysis, nd levels of copper nd zinc in serum, were obtined on dmission to the motel nd gin on dischrge from the motel on study dy 7. These tests were ll performed with stndrd methods by Roche Biomedicl, Richmond, V., in tril 1 nd by Roche Biomedicl, Rritn, N.J., in tril 2. Infection rtes were determined by virl isoltion in both trils nd /or by documenttion of fourfold or greter rise in serum-neutrlizing-ntibody titer in pired specimens obtined on the dy of virl chllenge nd 21 dys lter in tril 1. Nsl wsh specimens were collected before virl inocultion nd on the morning of ech dy, beginning with study dy 2 nd continuing through study dy 7. Nsl wsh specimens were collected in tril 1 by instilling 2 to 3 ml of 0.85% sline solution into ech nostril nd then collecting the effluents. This process ws repeted until minimum volume of 4 ml hd been obtined, which ws mixed with 1 ml of virus-collecting broth. In tril 2, 5 ml of lctted Ringer solution ws instilled into ech nostril, nd the effluent ws collected. Virl cultures were grown by stndrd methods in humn embryonic lung cells (WI-38) nd MRC5 cells in tril 1 nd in MDCK cells nd humn foreskin fibroblst (HFF) cells in tril 2 (7). Successive 10-fold dilutions of the nsl wsh specimens were mde nd cultured in HFF cell cultures to determine rhinovirl titers of ech specimen in tril 2. Mesurement of side effects. Subjects were sked ech dy bout the presence of side effects. On the finl dy of the study, ech subject completed questionnire regrding tste, ftertste, nd ny dverse effects of the mediction, in ddition to whether he believed he ws given ctive mediction nd not plcebo. Vitl signs were recorded dily. Sttisticl nlysis. The dt were collected mnully nd entered into VAX computer, verified by seprte opertor, nd then checked for logic, consistency, nd rnge before nlysis by using n SAS sttisticl pckge (11). Differences in ctegoricl vribles were tested by mens of the chi-squre or Fisher exct test (two-tiled). Continuous vribles were compred by using Student's t test. Ordinl vribles, such s the cold symptom scle, were nlyzed by using the Wilcoxon rnk sum test (11). An lph level of P s 0.05 ws used for defining the sttisticl significnce of differences between tretment groups. Significnt results with the ssocited probbility vlues re indicted in the tbles. For nonsignificnt results, probbility vlues re not shown. The smple size of 32 in tril 1 possessed 72% sttisticl power to demonstrte the 40% reduction in symptoms reported in the study by Eby et l. (4). Tril 2 possessed 83% power to demonstrte similr reduction. RESULTS Tril 1. In tril 1, 19 (56%) of the subjects (8 zinc, 11 plcebo) were women. Of the 32 volunteers, 27 were students (14 zinc, 13 plcebo). Only four of the subjects were smokers (2 zinc, 2 plcebo). The men ge ws 21.4 (+ 0.6, stndrd error of the men [SEM]) yers in the zinc group nd 20.6 (±0.5, SEM) yers in the plcebo group. The zinc gluconte nd plcebo groups demonstrted equivlent infection rtes of 100 nd 94%, respectively (Tble 1). All of the infected subjects except for one plcebo recipient, who only seroconverted, shed rhinovirus type 39. Only one individul, lso in the plcebo group, lcked ny evidence of infection by virl isoltion or seroconversion. The proportions of subjects who seroconverted were similr in the two tretment groups. Infected zinc recipients shed virus more consistently thn infected plcebo recipients during the study week, but the durtions of virl shedding fter chllenge were not significntly different.

3 VOL. 31, 1987 ZINC GLUCONATE LOZENGE THERAPY OF RHINOVIRUS COLDS 1185 TABLE 2. Illness, symptom scores, nd nsl mucus production in rhinovirus type 39-inoculted volunteers Type of tretment No. with % with colds of Nsl Totl Nsl Pper tissue (no. treted) colds (%) totl infected symptom score" symptom score" mucus wt count (gi5 dys)" (no.15 dys)" Zinc (16) 13 (81) (±1.3) 25.2 (±3.2) 31 (+8) 78.7 (±20.2) Plcebo (16) 12 (75) (±1.6) 21.5 (±3.8) 27 (+7) 49.9 (±13.7) " Dt represent the mens (± SEM). These clcultions included only infected subjects. Similr proportions of subjects developed colds in the two groups (Tble 2). A brekdown of symptom scores by ech study dy reveled significnt difference only on dy 7, with the zinc recipients hving more severe symptoms thn plcebo recipients. Zinc recipients showed trends towrd higher men mucus weight nd greter number of pper tissues used, but neither trend ws sttisticlly significnt. Perceptions were not significntly different regrding predominent lozenge tste nd pltbility or whether mediction ws ctive (Tble 3). The frequencies of dverse effects, such s nuse, mouth soreness, nd ftertste, were not significntly different between the two tretment groups. There were no significnt differences in vitl signs between the two tretment groups. Clinicl lbortory tests, including complete blood count, differentil leukocyte count, metbolic profile, urinnlysis, nd levels of copper nd zinc in serum, showed no significnt differences between the two groups except for n incresed men level of zinc in the serum of recipients of 105 versus 88 g of zinc per dl (P < 0.001, t = 4.40) (norml levels of zinc in serum re 70 to 150,ug/dl in the reference lbortory). Tril 2. In tril 2, 23 subjects were rndomly chosen to receive zinc nd 22 were rndomly chosen to receive plcebo, but one subject in the plcebo group ws shedding virus on dmission to the study nd ws thus excluded. Another subject ws excluded becuse of neuromusculr disorder noted fter rndomiztion to the plcebo group but before virl inocultion. Two more subjects dropped out of the zinc group becuse of fever nd nuse, respectively, on study dys 0 nd 2. Of the subjects, 41 completed the tril nd were vilble for nlysis. There were 13 men in the zinc group (62%) nd 9 men in the plcebo group (45%). Eight zinc recipients were smokers (38%), compred with six plcebo recipients (30%). The men ge ws 21.1 (± 0.6, SEM) yers in the zinc group nd 21.1 (± 0.4, SEM) yers in the plcebo group. In ech of the two groups (Tble 4), 19 subjects were infected. All 38 infected subjects shed rhinovirus type 13. Virl shedding ws slightly, but not significntly, more frequent in the infected plcebo recipients thn in the zinc recipients. Medin durtion of shedding nd geometric men virl titers were similr for the two groups (Tble 5). In the plcebo group, 16 subjects were judged to hve cold, s opposed to 13 in the zinc group. There were no significnt differences between the two groups in the frequency, severity, or durtion of ny individul cold symptoms. There were lso no differences in the rte or type of dverse rections between the two groups. DISCUSSION Zinc gluconte lozenge therpy beginning t the onset of cold symptoms hd no beneficil effect on experimentl rhinovirus type 39 colds in susceptible volunteers in tril 1. Prophylctic postexposure therpy, beginning 2 h fter experimentl inocultion of rhinovirus type 13, lso filed to show ny benefits. The proportions of volunteers with colds nd the durtions of colds were not different, nd the severities of cold symptoms were significntly different only during the lst dy of tretment during tril 1, with zinc recipients hving more severe symptoms on tht dy. The objective mesurement of nsl mucus weights ws lso slightly, but not significntly, greter in the zinc group in both trils. The rte, but not the durtion, of virl shedding ws significntly incresed in the zinc group in tril 1, nd there ws no difference in shedding titer, frequency, or durtion in tril 2. Zinc gluconte therpy ws begun 36 h fter virl inocultion in tril 1 nd 2 h fter inocultion in tril 2 to mximize the chnce of detecting therpeutic efficcy. The dosge of zinc gluconte used in this study ws selected in n ttempt to confirm results of the prior study by Eby et l. tht suggested efficcy of this dose in the tretment of nturl colds (4). Our formultions of zinc gluconte nd the mtching plcebo lozenges hd been previously studied to ssure comprbility nd effective blinding (Frr nd Gwltney, in press). The subjects in tril 1 showed no significnt differences in their perceptions of the two lozenges, nd hlf of the subjects in ech tretment group believed they were receiving ctive tretment. The filure to demonstrte zinc gluconte efficcy in this study my be interpreted in severl wys. It remins possible tht the result by Eby et l. (4) ws due to n effect ginst viruses other thn rhinoviruses but if so, it would be difficult to explin their drmtic results, given the fct tht rhinoviruses constitute the most frequent cuse of common colds, especilly during the fll, which ws the seson in which Eby nd collegues conducted their study. It would lso be difficult to explin why the zinc gluconte ws TABLE 3. Perception of lozenges by subjects No. of subjects (o) noting dominnt No. of tste s: subjects believing type No. of subjects noting tretment Pltbility of tretment ws: dverse effects (%) (no. treted) Sweet Sour Bitter Slty Uncertin scle" Active Plcebo Uncertin Nuse Sore Aftermouth tste Zinc (16) 7 (43.8) 7 (43.8) 1 (6.3) 0 (0) 1 (6.3) (+1.008) (37.5) 8 (50) 5 (31.3) Plcebo (16) 6 (37.5) 6 (37.5) 4 (25) 0 (0) 0 (0) (±1.287) (31.3) 8 (50) 2 (12.5) Pltbility scle involved selection of single number on + 10 (most plesnt) to -10 (most unplesnt) scle; dt given re the mens (+ SEM).

4 1186 FARR ET AL. ANTIMICROB. AGENTS CHEMOTHER. TABLE 4. Infection rtes, virl shedding, nd illness in volunteers inoculted with rhinovirus type 13 Type of tretment No. of subjects No. of virus- Medin durtion of No. of subjects with Men nsl (no. treted) shedding virus (%) positive dys" (%) shedding (dys) colds (% of subjects (g7 dys)' Zinc (21) 19 (90) 100 (75) 8 13 (68) 16.3 Plcebo (20) 19 (95) 113 (85) 8 16 (84) 14.3 Observtion dys on which virl culture ws positive for subjects who shed virus during study. b Medin durtion of virl shedding in dys fter chllenge. Virl cultures were done on study dys 2 to 8. c Men nsl mucus weights of subjects who shed virus. Tretment TABLE 5. Geometric men virl titers in nsl wsh specimens of volunteers who shed rhinovirus type 13 Virl titer (men ± SEM) on tretment dy: Zinc 15.9 ± 1.6 (13)b 38.0 ± 1.6 (18) 60.3 ± 2.1 (16) ± 1.8 (16) 9.6 ± 1.4 (14) 7.8 ± 1.6 (10) 5.6 ± 1.3 (13) Plcebo 14.5 ± 1.4 (13) 79.4 ± 1.6 (19) 47.9 ± 1.8 (19) 53.7 ± 1.7 (19) 20.0 ± 1.5 (16) 11.0 ± 1.4 (14) 11.5 ± 1.5 (13) 50% Tissue culture infective dose per ml. b Number of subjects with positive cultures for given study dy is given in prentheses. effective ginst other viruses but not ginst rhinoviruses, since previous in vitro dt hd suggested n ntirhinovirl effect (2, 9, 10). The negtive result in this study my be interpreted s hving been due to bet error, given the smll smple size of the two trils. However, we believe tht this is n unlikely explntion of this negtive result for severl resons. First, our trils hd considerble sttisticl power (72 nd 83%, respectively) to detect difference in the persistence of symptoms t 5 dys of the sme mgnitude s tht reported by Eby et l. (4). Thus, we re firly confident tht difference this lrge does not exist for these rhinoviruses. Our study involved the determintion of multiple ccepted outcome vribles, in ddition to symptoms (nsl mucus weight, number of pper tissues used, durtion of virl shedding, etc.). If zinc were truly effective, the cumultive power of detecting true difference in t lest one of these ccepted outcome vribles my hve been higher thn the power clcultions cited bove. Not only did these two trils fil to show trend in fvor of zinc for ny of these outcome vribles, but the zinc group ctully tended to fre slightly worse thn the plcebo group in terms of severl outcome vribles, including the more objective nsl mucus weights nd number of tissues used per dy. It is possible tht the difference between the results of this study nd the results of the study by Eby et l. (4) were due to bis in the ltter study. Eby nd collegues used unflvored zinc gluconte tblets nd unflvored clcium lctte tblets for lozenge therpy in their tril. Clcium lctte is reltively tsteless nd cn be esily distinguished on the bsis of tste from the rther unplesnt zinc gluconte. Becuse of higher rte of side effects nd higher dropout rte in the zinc group in the study of Eby et l., we re concerned tht their grossly dissimilr tblets could hve resulted in severl kinds of bis. Zinc tblets which tste bd my be more likely to be interpreted s ctive mediction, nd subjects believing they re being given ctive mediction my be more likely to give therpeutic credit to zinc tblets even in the bsence of true efficcy (Frr nd Gwltney, in press). It is further possible tht the noxious side effects of zinc my ct in some wy similrly to cupuncture in lessening the perception by the subject of the mild, resolving symptoms of common cold, resulting in colds of shorter durtion. It is likewise possible tht even if the subject notices the symptoms of the cold, he might be motivted not to report these symptoms so s to stop dministrtion of n unpltble, nuseting zinc tblet. In tril 1, which involved more tightly controlled experimentl sitution with documenttion of ech dose of mediction, 37% of subjects on zinc reported hving nuse nd 50% reported hving sore mouth. Recipients of zinc gluconte lozenge therpy did no better nd, in fct, did slightly worse in terms of severl outcome vribles in these two rndomized, plcebo-controlled, double-blind trils of therpy for experimentl rhinovirus infection. We conclude tht the previous study suggesting efficcy of zinc gluconte lozenges for tretment of the common cold my hve been bised becuse of the lck of mtching plcebo, with resultnt unblinding. The problem of bis becuse of unblinding ws noted by Chlmers to ccount for trend towrd efficcy in rndomized, controlled tril of scorbic cid tretment of common colds (3). The results of the present study suggest tht zinc gluconte should not be regrded s the long-sought cure for the common cold. ACKNOWLEDGMENTS This work ws supported in prt by Bristol Myers Products, Hillside, N.J. B.M.F. is the recipient of Milbnk Scholr Awrd in Clinicl Epidemiology from the Milbnk Memoril Fund, New York, N.Y. We cknowledge with grtitude the ssistnce of Ktherine F. Adms, Kthleen M. Kiehl, nd Pt P. Besley in conducting the volunteer study, Deborh F. Thcker nd Kte K. Engleby for technicl ssistnce, nd Mdeleine Wrd nd Mrjorie Jensen for ssistnce in the preprtion of the mnuscript. We lso grtefully cknowledge the help of Joseph Armellino, Joseph Miglirdi, George Blewitt, Niroo Gupt, nd their collegues t Bristol Myers Products nd Denis Schisno t Prgm Biotech, Inc., Bloomfield, N.J. LITERATURE CITED 1. Butterworth, B. E., R. R. Grunert, B. D. Kornt, K. Lonberg- Holm, nd F. H. Yin Repliction of rhinoviruses. Arch. Virol. 51: Butterworth, B. E., nd B. D. Kornt Chrcteriztion of the lrge picornvirl polypeptides produced in the presence of

5 VOL. 31, 1987 ZINC GLUCONATE LOZENGE THERAPY OF RHINOVIRUS COLDS 1187 zinc ion. J. Virol. 14: Chlmers, T. C Efficcy of scorbic cid on the common cold: n evlution of the evidence. Am. J. Med. 58: Eby, G. A., D. R. Dvis, nd W. W. Hlcomb Reduction in durtion of common colds by zinc gluconte lozenges in double-blind study. Antimicrob. Agents Chemother. 25: Geist, F. C., J. A. Btemn, nd F. G. Hyden In vitro ctivity of zinc slts ginst humn rhinoviruses. Antimicrob. Agents Chemother. 31: Gwltney, J. M., Jr., P. B. Mosklski, nd J. 0. Hendley Interruption of experimentl rhinovirus trnsmission. J. Infect. Dis. 142: Hmprin, V. V Rhinoviruses, p In E. H. Lennette nd N. J. Schmidt (ed.), Dignostic procedures for virl nd rickettsil infections, 5th ed. Americn Public Helth Assocition, Wshington, D.C. 8. Jckson, G. G., H. F. Dowling, I. G. Spiesmn, nd A. V. Bond Trnsmission of the common cold to volunteers under controlled conditions. I. The common cold s clinicl entity. Arch. Intern. Med. 101: Kornt, B. D., nd B. E. Butterworth Inhibition by zinc of rhinovirus protein clevge: interction of zinc with cpsid polypeptides. J. Virol. 18: Kornt, B. D., J. C. Kur, nd N. W. Hlcomb Zinc ions inhibit repliction of rhinoviruses. Nture (London) 248: SAS Institute Inc SAS user's guide: sttistics. SAS Institute Inc., Cry, N.C.