Measles aerosol vaccination

Measles ranks fifth among the five major childhood conditions which are responsible for 21% of all deaths in low and middle-income countries. Measles immunization is considered the most cost-effective public health intervention in the world. In recent years, there has been a critical need to identify alternative routes of measles immunization, which are rapid, reliable, cost-effective, needle-free, and suitable for use in mass campaigns. Aerosol administration of measles vaccines in mass campaigns was first proposed by Dr. Albert Sabin. We review the different clinical trials that have been conducted using the classic Mexican device as well as issues regarding vaccine strain, presentation, and manufacturer. Results of clinical trials indicate that the method is safe and immunogenic in infants and school age children. The viral inoculum will probably need to be increased when administered to infants. From the logistical point of view, the use of the aerosol method has not been evaluated in routine immunization although feasibility of its routine implementation was proved in mass campaigns in Mexico. Cost savings will probably be demonstrated. As to licensure, its compliance with the appropriate international regulatory requirements for medical aerosol delivery devices is in process.

Immunogenicity of aerosol measles vaccine given as the primary measles immunization to nine-month-old Mexican children

Aerosol measles vaccination has been found to be more immunogenic than subcutaneous administration as a booster in school aged children, and immunogenic in 12-month-old children as a primary dose. The objective of the study was to evaluate immunogenicity to aerosol measles vaccine in 9-month-old children.

METHODS

Nine-months-old infants received Edmonston-Zagreb measles vaccine by aerosol (10(3.58) CCID50/0.1 mL, estimated retained dose 10(2.81) CCID50 or subcutaneous route (10(4.28) CCID50/0.5 mL); cellular and humoral immunity and adverse events were assessed.

RESULTS

Measles-specific T cell proliferative responses developed in 42% of children given aerosolized vaccine compared with 67% of those who received subcutaneous vaccine (p = 0.01); the mean stimulation index (SI) was 4.4+/-0.7 versus 6.9+/-1, respectively, (p = 0.05). Seroconversion rates were 33 and 92% after aerosol or subcutaneous immunization (p < 0.001). Among infants who developed serologic responses, measles geometric mean titers (GMT; 95% CI) by neutralizing antibody assay were 215 mIU/mL (115-400) in aerosol vaccine recipients and 411 mIU/mL (345-490) in those given subcutaneous vaccine (p = 0.06).

CONCLUSIONS

The proportion of 9-month-old infants who developed cellular and/or humoral immunity to measles was lower in the aerosol group but measles antibody and T cell responses were comparable among those who developed measles immunity. Differences in response rates are attributable to the lower aerosol dose. Improving aerosol delivery or increasing the dose may enhance immunogenicity of primary aerosol measles vaccination in this age group.

Induction of Cellular and Humoral Immunity after Aerosol or Subcutaneous Administration of Edmonston‐Zagreb Measles Vaccine as a Primary Dose to 12‐Month‐Old Children

Infants were immunized by aerosol (10(3.6) plaque-forming units [pfu]/dose) or subcutaneous (sc) (10(4.27) pfu/dose) administration of Edmonston-Zagreb measles vaccine. Measles-specific T cell proliferative responses with a stimulation index of > or =3 developed in 72% of children given aerosol-administered vaccine, compared with 87% given s.c.-administered vaccine (P =.06). Seroconversion rates were 90% after aerosol-administered vaccine and 100% after s.c.-administered vaccine (P=.01), and measles geometric mean titers were 237 milli-international units (mIU) (95% confidence interval [CI], 146-385 mIU) and 487 mIU (95% CI, 390-609 mIU) in each group, respectively (P=.01). Measles-specific T and B cell responses were weaker after aerosol than after sc vaccination, indicating a need to use a higher aerosol dose to achieve optimal immunogenicity.

A randomized trial demonstrating successful boosting responses following simultaneous aerosols of measles and rubella (MR) vaccines in school age children

The reactogenicity and immunogenicity of combined measles and rubella (MR) booster vaccination, via aerosol and subcutaneous routes, was assessed in 562 healthy children. Rates of rubella seroconversion and geometric mean titers (GMT) were similar for both routes. Rates of measles PN seroconversion, GMT and measles ELISA post-vaccination seropositivity and seroconversion rate were each higher for aerosol vaccine (54%, 3928 IU/l, 99.6 and 98.8%), than for subcutaneous vaccine (7%, 866 IU/l, 92.2 and 82.4%) (P<0.01). Reactogenicity was higher for subcutaneous vaccine (P<0.05). This study demonstrates that aerosol vaccine was more immunogenic for measles antibodies, and equally immunogenic for rubella antibodies. Aerosol vaccine was less reactogenic.

[The ABCs on anthrax for health personnel]

The purpose of this series of articles is to present to health personnel an updated summary on bioterrorism associated agents. In this first article an updated summary on anthrax is presented. Emphasis has been placed on the characteristics of cases which occurred during October in the United States of America and on the experience of governmental agencies of that country to face the emergency. Measures implemented in Mexico are described as well. The authors are convinced that the best arm against terror is timely and updated information.

[Drug resistance of Mycobacterium tuberculosis in Orizaba, Veracruz. Implications for the tuberculosis prevention and control program]

BACKGROUND

Tuberculosis, declared a global emergency by the World Health Organization, continues to be an important public health problem in Mexico, included in the first twenty causes of death.

OBJECTIVE

To know the impact of drug resistance of Mycobacterium tuberculosis on treatment outcome, need of re-treatment and mortality in a cohort of patients with pulmonary tuberculosis receiving directly observed therapy, short course (DOTS).

METHODS

We conducted a population-based study in a suburban region in Southern Mexico. People who had been coughing for more than two weeks underwent sputum acid-fast bacilli smear. Patients with a positive smear were recruited and underwent clinical exam, chest X-ray, HIV testing, and sputum cultures. Identification, drug susceptibility testing and restriction fragment length polymorphism analysis (RFLP) were performed in all isolates. Patients were followed every 12 months for new episodes of tuberculosis and vital status. Patients were referred for clinical care to the local program of tuberculosis. Deaths were corroborated with death certificates. Informed consent was obtained from participants.

RESULTS

Between March 1995 and February 1999, tuberculosis was diagnosed in 371 patients who were followed for an average of 32 months. M. tuberculosis was cultured from 316 patients; resistance to any drug occurred in 25.0% of isolates (primary 18.8%, acquired 49.2%); only to isoniazid in 6.8% (primary 7.3%, acquired 4.8%); to isoniazid and rifampin in 6.2% (primary 1.6%, acquired 23.8%). Patients with drug resistance had a higher probability of treatment failure (OR = 16.9, CI 95% 4.5-63.0) and patients with MDR strains had a higher probability of need of re-treatment (RR = 24.4, CI 95% 8.8-67.6), and of death (RR = 4.0, CI 95% 1.5-10.7). Additional variables were found to be associated with subsequent episodes of disease and mortality: Cocaine use, chronic disease, type of radiological lesions, HIV co-infection, non-compliance and treatment delay, as well as RFLP clustering.

CONCLUSIONS

In this study, we observed that drug resistance showed a severe impact on the outcome and survival; drug-resistance was the most significant factor for these negative outcomes; DOTS may not be sufficient in areas where drug resistance is considerable, and patient follow-up for longer periods of time, as compared to evaluation at the end of treatment, provides additional information which is useful for prevention and control programs.

Nosocomial infections in a community hospital in Mexico

Results from prospective surveillance of nosocomial infections (NIs) in a small community hospital were evaluated, and a case-control study was conducted. The rate of 1.4 NIs per 100 discharges determined by prospective surveillance was found to be underestimated. Prematurity, pediatric service, surgery, length of stay, and age were independently associated with NI.

Factors associated with tuberculin reactivity in two general hospitals in Mexico

OBJECTIVE

To identify risk factors associated with tuberculin reactivity in healthcare workers (HCWs).

DESIGN

Cross-sectional survey of tuberculin reactivity (2 TU of purified protein derivative (PPD) RT23, using the Mantoux two-step test).

SETTING

Two general hospitals located in a region with a high prevalence of tuberculosis and high bacille Calmette-Guerin (BCG) coverage.

PARTICIPANTS

Volunteer sample of HCWs.

RESULTS

605 HCWs were recruited: 71.2% female; mean age, 36.4 (standard deviation [SD], 8.2) years; 48.9% nurses, 10.4% physicians, 26.8% administrative personnel; mean time of employment, 10.9 (SD, 6.7) years. PPD reactivity (> or =10 mm) was found in 390 (64.5%). Multivariate analysis revealed an association of tuberculin reactivity with occupational exposure in the hospital: participation in autopsies (odds ratio [OR], 9.3; 95% confidence interval [CI95], 2.1-40.5; P=.003.), more than 1 year of employment (OR, 2.4; CI95, 1.1-5.0; P=.02), work in the emergency or radiology departments (OR, 2.0; CI95, 1.03-3.81; P=.04), being physicians or nurses (OR, 1.5; CI95, 1.04-2.11; P=.03), age (OR, 1.04; CI95, 1.02-1.07 per year of age; P<.001), and BCG scar (OR, 2.1; CI95, 1.2-3.4; P=.005).

CONCLUSIONS

Although the studied population has a high baseline prevalence of tuberculosis infection and high coverage of BCG vaccination, nosocomial risk factors associated with PPD reactivity were identified as professional risks; strict early preventive measures must be implemented accordingly.

Mycobacterium tuberculosis drug resistance in a suburban community in southern Mexico

OBJECTIVE

To determine the impact of drug resistance (DR) on the clinical outcome and transmission of tuberculosis under programmatic conditions.

METHODS

Prospective cohort and molecular epidemiologic study in the Orizaba Health Jurisdiction of Mexico. Between March 1995 and July 1999, chronic coughers with positive acid-fast bacilli (AFB) detected in sputum smear underwent clinical and mycobacteriologic evaluation (species identification, drug susceptibility testing and IS6110-based genotyping). Treatment was provided in accordance with official norms.

RESULTS

Mycobacterium tuberculosis was isolated from 326/387 AFB-positive cases. The rate of DR was 24.2% and that of multidrug resistance (MDR, defined as resistance to both isoniazid and rifampin at least) was 7.7%; 78% were cured, 8% abandoned treatment, 6% failed treatment, and 5% died. An additional 13.5% received retreatment and 8.9% died during a median 28.6 months of follow up. Factors associated with DR by multivariate analysis were chronicity of tuberculosis (OR 4.8, 95%CI 2.7-8.4, P < 0.001), age >40 years (OR 1.9, 95%CI 1.1-3.2, P = 0.02) and indigenous origin (OR 0.3, 95%CI 0.13-0.75, P = 0.01). Cox-adjusted relative risks showed that MDR (RR 2.5, 95%CI 1.02-6.16, P = 0.04), HIV infection (RR 31.3, 95%CI 11.6-84.8, P < 0.001), and chronicity of tuberculosis (RR 2.1, 95%CI 1.0-4.4, P = 0.06) were associated with mortality, controlling for age. Predictors of retreatment were DR (not including MDR) (RR 2.2 95%CI 0.89-5.31, P < 0.087), MDR (RR 12.6, 95%CI 5.46-28.88, P < 0.001), and living in a household with an earthen floor (RR 2.8, 95%CI 1.27-6.13, P = 0.011). Being infected with MDR-TB was the only factor associated with a decreased likelihood of being in an RFLP cluster (OR 0.31, 95%CI 0.12-0.81, P = 0.02).

CONCLUSIONS

Although MDR-TB may have a decreased propensity to spread and cause disease, it has a profoundly negative impact on tuberculosis control.

Underestimation of Mycobacterium tuberculosis infection in HIV-infected subjects using reactivity to tuberculin and anergy panel

BACKGROUND

This study aimed to evaluate purified protein derivative (PPD) reactivity and its interrelationship with anergy panel and CD4+ lymphocytes in HIV-infected subjects as compared to PPD reactivity in HIV-uninfected individuals in a tuberculosis endemic and high Bacillus Calmette-Guérin (BCG) coverage environment.

METHODS

Clients of four Mexico City HIV detection centres were screened for HIV-1 antibodies (ELISA or haemagglutination, Western Blot); reactivity to PPD (Mantoux PPD, 5TU RT-23), Candida (1:1000, 0.1 ml), and tetanus toxoid (10Lf, 0.1 ml); and CD4+ T cells. Active tuberculosis was excluded. Informed consent was obtained.

RESULTS

From 5130 clients 1168 subjects were enrolled; of these 801 (68.6%) were HIV positive. Reactivity to PPD among HIV-positive subjects was found in 174 (22%), 261 (32.6%), and 296 (37%), at PPD cutoff levels of > or =10 mm, > or =5 mm, and > or =2 mm as compared to 224 (61%) of 367 HIV-negative individuals' reactors to PPD (> or =10 mm) (P < 0.001). After exclusion of anergic individuals using two cutoff levels for cutaneous allergens (< or =2 mm and < or =5 mm), PPD reactivity between HIV-infected and uninfected individuals continued to be significantly different. Only HIV-infected individuals with CD4+ T cells > or =500 cells/mm3 had similar reactivity to PPD as HIV-uninfected individuals. Variables associated with PPD reactivity were CD4+ T cell counts, BCG scar, HIV infection and age.

CONCLUSIONS

PPD reactivity was useful to diagnose tuberculosis infection only among HIV-infected individuals with CD4+ counts > or =500 cells/mm3. Among individuals with lower counts, lowering cutoff levels or using anergy panel did not permit comparable reactivity as that observed among HIV-uninfected individuals.

Clinical consequences and transmissibility of drug-resistant tuberculosis in southern Mexico

BACKGROUND

Consequences of drug-resistant tuberculosis (TB) in developing countries using directly observed treatment, short-course (DOTS), are not well defined.

OBJECTIVE

To determine the impact of drug resistance on clinical outcome and transmission of TB under programmatic conditions.

PATIENTS AND METHODS

A prospective cohort and molecular epidemiologic study was conducted in southern Mexico. Between March 1995 and February 1998 all patients with persistent cough whose sputa had acid-fast bacilli (AFB) underwent clinical and mycobacteriologic evaluation (species identification, drug susceptibility testing, and IS6110-based genotyping). Treatment was provided in accordance with Mexico's National Tuberculosis Program. Clinical and microbiologic outcomes and molecular epidemiologically defined transmission were measured.

RESULTS

Mycobacterium tuberculosis was isolated from 238 of the 284 AFB smear-positive persons. The overall rate of resistance was 28.4% (new, 20.7%; retreated, 54.7%), and 10.8% (new, 3.3%; retreated, 35.8%) had multi-drug-resistant TB (ie, resistance to isoniazid and rifampin). After treatment, 75% (new, 81.0%; retreated, 52.8%) were cured, 8% (new, 7.8%; retreated, 7.5%) abandoned therapy, 9% (new, 3.9%; retreated, 28.3%) had treatment failure, and 4% (new, 3.3%; retreated, 7.5%) died. Another 2% of patients relapsed, and 9% died during a median of 24.4 months of follow-up. Drug-resistance was a strong independent risk factor for treatment failure. Being infected with multi-drug-resistant TB was the only factor associated with a decreased likelihood of being in a restriction fragment length polymorphism cluster.

CONCLUSIONS

Despite the use of DOTS, patients with drug-resistant TB had a dramatically increased probability of treatment failure and death. Although multi-drug-resistant TB may have a decreased propensity to spread and cause disease, it has a profoundly negative impact on TB control.

The role of core groups in transmitting Mycobacterium tuberculosis in a high prevalence community in Southern Mexico

SETTING

A community in Southern Mexico with a high prevalence of tuberculosis.

OBJECTIVE

To characterize the transmission dynamics in a region with a DOTS-based tuberculosis control program.

DESIGN

Community-based screening of chronic coughers between 1 March 1995 and 31 August 1996. Individuals with acid-fast bacilli (AFB) in their sputum were enrolled, interviewed, and had mycobacterial cultures and fingerprinting performed. In-depth interviews were conducted on all persons with DNA fingerprinting.

RESULTS

AFB smears were performed on 1424 individuals, 124 of whom were microbiologically confirmed. Of the 95 cases for whom bacterial DNA fingerprints were available, 38 were in clusters. The largest cluster involved seven individuals who were members of a social network centered on a series of unlicensed bars.

CONCLUSION

This population-based molecular epidemiologic study showed that a focus of transmission within a social network accounted for one fourth of transmission which rapidly progressed to disease. These observations raise questions about the potential benefit of targeted tuberculosis control interventions in health jurisdictions approaching WHO-defined DOTS benchmarks.

Tuberculosis epidemiology and control in Veracruz, Mexico

BACKGROUND

Tuberculosis (TB) rates remain high in regions of Southern Mexico despite the existence of a National Tuberculosis Program. Understanding TB epidemiology in such settings would assist in the design of improved TB control and highlight the challenges confronting TB control in developing countries.

METHODS

We conducted a retrospective review of treatment control cards from 1991 to 1994 in five municipalities in a semiurban region of Southern Mexico.

RESULTS

The relatively high rate of TB observed, 42.6 per 100,000 inhabitants, did not change significantly during the study period. Cure rates among new cases were 79% and significantly lower among retreatment cases (62%). Directly observed therapy (DOT) was administered to 84% of patients. Approximately one-half of the retreatment cases who were not cured were compliant with therapy, suggesting that drug resistance contributed to these poor results. Of particular concern was a core group of 16 patients who had received at least three treatments.

CONCLUSIONS

This region of Mexico has persistently high TB rates despite a DOT-based TB control programme which achieves an overall cure rate of 77%. There exist many retreatment cases for whom cure rates are significantly lower. These cases may serve as a core group for the dissemination of drug resistant TB. The control programme is being reinforced by a nominal register of patients, decreasing administrative barriers for drug supply to individual patients and the availability of mycobacteria cultures. In addition to these measures, in regions which are approaching the levels of efficacy recommended by the WHO it may be appropriate to consider focusing efforts on the identification and treatment of chronic cases.

[Efficacy and efficiency of antitubercular treatment in health jurisdictions of Morelos]

OBJECTIVE

To evaluate the efficacy and efficiency of tuberculosis treatment administered by the Secretaría de Salud (SSA) in the sanitary jurisdictions of Cuernavaca and Cuautla, Morelos, for the 1992-1996 period by retrospectively reviewing tuberculosis treatment control cards.

MATERIAL AND METHODS

Official Norm for Tuberculosis Prevention and Control in Primary Care Units outcome definitions were used. Data was collected on standardized forms and analyzed with SAS and Epi Info programs; 149 primary care units and 4 hospitals in the study area were visited.

RESULTS

There were found 288 patients cards, of which 260 were new cases. These patients received 311 treatments of which 85% were directly observed. Reviewed cards represented 60% of SSA notified cases for this period. There were analyzed 246 treatments of which 32% were bacteriological cures, 26% probable cures, 18% dropouts, 1% failures and 3% deaths. In 20% of treatments the outcome was unknown. Cure rate was better in new cases (61%) than in retreatments (38%), p < 0.01. Efficacy of treatment was 71% and efficiency 58%. Patients receiving retreatment abandoned it more frequently (32%) than new cases (16%), p < 0.01. A statistically significant association was found between abandoned treatment and being retreated (OR = 3.3, CI 95% 1.3-8.5, p = 0.01) or belonging to a lower socioeconomic level (OR = 2.3, CI 95% 1.0-4.9, p = 0.04). In the 34 retreatment programs, 22 were initiated after abandonment, failure or relapse.

CONCLUSIONS

Proportion of cure rate (58%) compares unfavorably with WHO recommendations (85%). Implications of a high dropout rate and probability of circulation of resistant strains of M tuberculosis are discussed. Creative strategies to reinforce patient compliance which take into account the patient and not only the health services, extension of cultures to known M. tuberculosis drug resistance and evaluation of modifications to drug regimens are proposed. Review of treatment control cards is a useful tool for program evaluation.

[Measles vaccination by the aerosol method in Mexico]

The present work describes the anti-measles vaccination program by the inhaled aerosol method undertaken in Mexico between 1988 and 1990. Detailed descriptions are given of the equipment, staff, training programs, promotion and campaigns. The vaccine is specified: Edmonston-Zagreb strain cultured in diploid cells at the Instituto Nacional de Virología of the Secretaría de Salud in Mexico with titres varying from 1045 plaque forming units (PFU/ml) to 1048 PFU/ml administered in a 30 sec inhalation with aerosol. During this exposure period, 2800 to 4000 PFU per child are estimated to enter the child, of which approximately 25% is the retained doses, i.e. 700 to 1000 PFU/child. A total of 3760684 children of school and pre-school age have been vaccinated in 13 of the 32 federal entities of the country. No undesirable effects of any importance were observed, and the limited serological and field studies support the effectiveness and security of this method. On the other hand, the method is much cheaper, faster and better accepted by the population than the subcutaneous injection.

[Sexually transmitted diseases and the HIV/AIDS epidemic]

Studies on sexually transmitted diseases (STD) during the previous years in Mexico are discussed. The information sources were: a) Surveys among commercial sex workers. Since 1990, 1,386 women have been studied in four federal states through structured questionnaires and laboratory tests. Prevalence of different STD's has been significant (syphilis (VDRL, FTA-abs) 23.7%; chlamydiosis (Ag IF) 12.9%; gonorrhea (Ag, ELISA) 11.5%; anti-HBs 11.0%; herpes 1,2 (IgM) 9.3%, HBsAg 5.7%. Frequency of HIV (ELISA, Western blot) has been low; 0.5%. In 1994, 662 women were studied in Mexico City, with different laboratory techniques for chlamydiosis and gonorrhea (culture), hepatitis B (anticore antibodies) and herpes (total antibodies) with the following results: syphilis 1.5-12%; chlamydiosis 10.8-11.7%; gonorrhea 0-5.9%; hepatitis B 0-7.1%; herpes 44.7-78%; and HIV 0-1.4%. b) Surveys among men with homosexual and bisexual practices. 325 subjects have been studied in three federal states using methods similar to those of the 1990 survey. Contrasting with results among women, HIV prevalence was found to be high; (18.8%), and considerable for other STD's: anti-HBsAg 28.6%, syphilis 34.9%, recent herpes 10.9%, HBsAg 5.0%, chlamydiosis (Ag, IF) 4.3%, herpes simplex 1,2 (Ag, IF) 4.7%, gonorrhea (Ag, ELISA) 2.8%. c) Patient clinical studies. The clinical interrelationship between different STD and HIV infection has been studied; clinical differences are described between patients with condylomata or syphilis depending on HIV serostatus. Implications of the interrelationship between different STD's and HIV infection for the prevention and control of these diseases are discussed.

[AIDS cases in the rural area in Mexico]

The objective of this paper is to describe the AIDS epidemic in rural areas of Mexico. Information from the National AIDS Registry and the 1990 XI National Census was used. Rural AIDS cases and urban cases were compared regarding notification time, sex, risk categories and migration information. Of the 19,090 AIDS cases reported to the first of July 1994, 699 (3.7%) were rural cases. The first five of these cases were reported in 1986, three years after the first cases had been reported in Mexico. The number of AIDS cases has been growing each year but in 1991. Cases have been reported by all Mexican states. The state with the highest prevalence was Nayarit with 102 cases per million inhabitants, followed by Morelos with 99, Jalisco with 90, and Colima and Tlaxcala with 84. A total of 25% of the rural cases are migrants who have been to the US, against 6.1% of cases from urban areas. The distribution by sex shows 21.3% of women affected against 14.4% of urban cases (p < 0.05). The rural female to male ratio is 1:4, while the urban ratio is 1:6. The prevalence rates are almost three times greater in men than in women. The rural AIDS pattern represents a problem not because of the number of people affected but because of the heterosexual way of transmission. We do not think that migration to the US is going to change. The rural AIDS epidemic is more recent and growing faster than that occurring in the urban setting.

[Tuberculosis and AIDS in Mexico]

Tuberculosis (TB) still is an important health problem in Mexico. According to reported figures, an excess in the number of cases has occurred during recent years, mainly among young adults of both sexes. The present estimated rate of TB is 51.7 cases/100,000 inhabitants. This is the most frequent endemic infection among AIDS patients, ranking third among infectious diseases after candidiasis and P. carinii pneumoniae. A total of 8.3% of the 19,352 AIDS cases notified to July 1994, presented TB as the initial manifestation. According to sentinel surveillance carried out since 1990 in 17 states, HIV seroprevalence among TB patients has been 3.1% (0-6.5%) in males and 1.0% (0-2.3%) in females. Results of epidemiologic research in the field of TB prevention and characteristics of drug sensitivity of strains of M. tuberculosis isolated from HIV/AIDS patients are also described. Finally, perspectives of TB prevention and control are discussed.

[The strategy for preventing HIV/AIDS transmission via the blood and its derivatives in Mexico]

This study presents blood-associated AIDS epidemic trends in Mexico, including cases due to blood transfusions, cases in professional blood donors and hemophiliacs. We present also an overview of preventive measures--both legal and educative--undertaken to prevent this type of transmission and its effects on the epidemic. The first blood-associated AIDS cases in Mexico were reported in 1985, since then and up to July 1, 1994 a total of 1,728 adult cases and 116 pediatric cases have been reported (12.3% and 25% of the total cases, respectively). As in many other parts in the world, in Mexico women were markedly affected by this form of transmission; the women to men morbidity ratio is 1.35. Another group particularly affected by AIDS in Mexico are professional blood donors, who were infected because of improper management and recycling of blood transfusion centers bank materials such as plasmapheresis sets, in some blood transfusion centers in our country. Blood screening is mandatory for all blood donors in Mexico since May, 1986. A year later blood commercialization was banned because of the extremely high HIV infection prevalences found in some professional blood donors (7.2%). Since that time a whole set of preventive measures has been implemented in our country, including blood quality and safety control as well as educative interventions. Results of these measures began to become evident by the end of 1991, when newly reported blood associated AIDS cases started to decrease, as opposed to their continuous growth seen in previous years. Up to July 1, 1994 we estimate that a total of 2,750 AIDS cases have been prevented through these measures, recovering an average of 36 years of potential life for each of them. Although blood transmission preventive measures have rendered significant achievements, we still have to face some very complex challenges such as potential ruralization of the epidemic and its impact on HIV infection prevalences among potential blood donors and therefore the need to ensure blood screening in rural areas.

[The epidemiology of AIDS/HIV in Mexico: from 1983 to March 1995]

The purpose of this study is to analyze the HIV/AIDS magnitude, distribution, frequency, patterns, trends, risk factors, risk groups, estimation and evaluation of interventions in Mexico during the last twelve years. Results of a summary of statistics and results from several sources are presented including the National Registry of AIDS cases, HIV sentinel surveillance in 18 cities of the country, analysis of death certificates, cross-sectional, longitudinal, observational, and intervention studies. As of March 1995, 34,230 AIDS cases, 120,000 HIV infections and 21,000 AIDS deaths are estimated. A damaged exponential growth with duplication of AIDS cases every 18 months can be seen. Epidemiological patterns of transmission are found primarily among men with homosexual and bisexual practices. The male:female ratio is 6 to 1. In 1992 AIDS was the 19th cause of death among the general population. At least two patterns of transmission have been identified: one is the western-urban pattern which contributes with more than 90% of cases and the other, more recent, has been described as Caribbean-rural. Blood transmission of AIDS shows a downward trend, and heterosexual and perinatal transmission is slightly increasing. Seroprevalence among adults is 0.06%: however, among groups with risk practices, rates up to 50% have been found. Risk factors are similar to those described in the literature in other countries, and have been used for designing interventions. Evaluation of interventions has been accomplished by demonstrating positive results in the prevention of blood transmission and sexual transmission among female commercial sex workers; prevention efforts directed to men with homosexual practices have not been successful. Between 77,000 and 88,000 cumulated AIDS cases are estimated in Mexico for the year 2000.

[The HIV/AIDS epidemic and women in Mexico]

This study presents an analysis of AIDS cases and seroprevalence of HIV infection among Mexican women, from the onset of the epidemic through June 1994, as well as the analysis of the social and cultural factors that put women in a powerless situation regarding the adoption of preventive measures. Since 1985, when the first AIDS cases among women were reported in Mexico and until June 1, 1994, a total of 2,767 cases have been reported, representing 14.8% of the total number of cases. The first cases of AIDS among women were associated to infected blood transfusions; however, in 1986, heterosexually transmitted cases began to appear. Currently, only 35% of newly reported AIDS cases are associated to blood transfusions while 64% of them are related to heterosexual transmission. In fact, two epidemics are evident: one transmitted through blood, showing a downward trend (duplication time 45 months), and a second one, heterosexually transmitted, increasing twice as fast (duplication time 27 months). The latter is expected to dominate AIDS epidemiology among women in the future. In general, women are more vulnerable to HIV/AIDS biologically, but also socially and culturally. Women's economic, social and cultural subordination to their sexual partners results in a situation that makes it difficult for them to assess their infection risk and even more, to negotiate taking preventive measures. This situation is even more disadvantageous to rural women and, together with the recent trend of the AIDS epidemic to ruralization and with internal and international migration (temporary work force migration to the USA), can result in deep demographic and social effects. We conclude that it is necessary to work on the design and assessment of preventive measures under women's control, that empower them to protect themselves even without their partner's awareness. Also, it is necessary to promote sexual education among young heterosexual couples on how to talk about sexual issues and negotiate the use of preventive measure according to their actual sexual practices.

[Identification of enterotoxins and cytotoxins of Escherichia coli by Vero cell culture and solid-phase hybridization (colony blot)]

We studied 40 E. coli strains from meat and hamburger and 64 strains from stools of people: 14/64 from traveler's diarrhea and 50/64 from infants with and without diarrhea. We want to know if they could be producing of cytotoxin and enterotoxin in Vero culture cells as well as phenotypic and genotypic relationships. The serotypes that we isolated were different than O:157H:7. We found 3 cytotoxic strains, 77 heat labile enterotoxic strains on Vero culture cells, and 19 E. coli strains with cytotoxin and LT enterotoxin. One strain isolated from infant with diarrhea was negative sorbitol but cytotoxic effect and it was O:55 serotype. The colony blot and cytotonic were found in 90 (86.5%) E. coli strains. The sensitivity of colony blot was 93.75%.

[Cytotonic and cytotoxic effect of cholera toxin on Vero cells and its relation to PCR]

We studied 40 Vibrio cholerae strains: 16 from stool, 16 from sewage and 8 from food. The serotypes were Inaba in 21 strains, 8 Ogawa strains and 11 V. cholerae non-O1. PCR was made with ctx2 and ctx3 primers with 25 cycles of temperature: 1 min at 94 degrees C, 1 min at 60 degrees C and 1 min at 72 degrees C. 24 V. cholerae strains were positive: 18/24 Inaba y 6/24 Ogawa. PCR was negative for 16 strains: 3 Inaba serotype, 2 Ogawa y 11 V. cholerae non-O1. In Vero culture cells 18 strains were cytotonic, 21 cytotoxic and 1 strain was negative. ELISA was positive for 11 strains with PCR positive. The PCR sensitivity was 95.83% compared with culture cells. V. cholerae O1 produced cytotoxic effect on Vero culture cells, maybe related to ACE factor. Colony blot was made with a specific probe labeled with digoxigenin and it could detect 4 Vibrio cholerae toxigenic strains with PCR negative. All V. cholerae Non O1 strains were PCR negative.

[Phenotypic and genotypic characterization of Vibrio cholerae O1]

We made 52180 tests for isolation and identification of toxigenic V. cholerae O1 from rectal swabs and reference strains. We isolated 17.6% V. cholerae O1 strains in 1991, 43.5% in 1992 and 38.9% in 1993. The main serovar in 1991 was Inaba, whereas in 1993 a similar percentage was serovar Ogawa. The phenotype of V. cholerae strains was determined by hemolysis test, Voges-Proskauer test, polymyxin B resistance and phages 4 and 5 resistance. All of the mexican strains were El Tor. There were 2.9-0.75% hemolytic strains from 1991 to 1993, but they were negative when the test was made in tube with human erythrocytes. The resistotypes were performed in 24526 selected strains by Kirby-Bauer method and MIC tests. All of the strains were sensitive, except more than 100 strains isolated in Veracruz that were resistant to tetracycline and doxycycline. Detection of cholera toxin was made by ELISA and on culture of Vero and CHO cells. All the V. cholerae O1 strains were toxigenic. The genotype was determined by PCR and ribotyping. The PCR amplified one 564 pb fragment on V. cholerae O1. The ribotypes of mexican strains were 5 and 6a.

[Polymerase chain reaction (PCR) for the identification of toxigenic Vibrio cholerae O1 in oysters]

PCR was made with ctx2 (CGG GCA GAT TCT AGA CCT CCT G) y ctx3 (CGA TGA TCT TGG AGC ATT CCC AC) primers for subunit A of cholera toxin, 30 cycles of temperature on samples of 50 g of oysters added in 450 ml of peptone alcaline water that were inoculated with 15 x 10(6), 0.75 x 10(6) and 0.15 x 10(6) CFU/ml of toxigenic 6707 V. cholerae O1 reference strain. The samples were tested by three microbiological methods: INDRE's method uses 1 x 10(-1) dilution of sample, two fold pass to peptone alcaline water pH 9 incubated 18 h and 6 h at 37 degrees C, the Food and Drugs Administration (FDA) method uses 10(-1) to 10(-6) dilutions of sample, 6 h incubation and reincubation for 18 h at 37 and 42 degrees C and the Mexican laboratories (LMD) with 10(-4) to 10(-3) dilutions, the samples were incubated for 6 h and then reincubated for 18 h at two temperatures 37 and 42 degrees C. The PCR by INDRE's method was positive with 3 x 10(2) CFU/ml/g oyster. In the FDA's method the PCR detected DNA in 10(-4) dilution with 3 x 10(1) CFU/ml/g oyster and in LMD's method the PCR was positive in 10(-3) with 3 CFU/ml/g oyster. The results of the PCR were obtained between 5-6 h, and later V. cholerae O1 was isolated by three microbiological methods. The PCR reproducibility was better on DNA sample diluted 1:4 and 10 microliters of sample increased from 1:1000 to 1:10000 the sensitivity of PCR.

[Cytotoxic effect of Vibrio cholerae non-O1 on Vero cells]

At the present time there is still in Mexico a diarrhoeal outbreak due to Vibrio cholerae O1. In INDRE we have isolated from the same outbreak last year (jan-apr), 70 strains of Vibrio cholerae Non-O1. These were isolated from patients with a diarrhoeal illness different from cholera. Patients were of different ages and sex, and from various geographic areas. The isolated strains were confirmed by serological agglutination test with polyclonal antisera, and they neither belong to O1 serogroup or O139. We assayed all the 70 strains in Vero cells, searching for cytotoxic effect, probably attributed to cholera toxin, or any other toxin. The strains were screened by PCR for cholera toxin gene detection, and negative results were obtained. We have found only one CT-producer strain, but it was a rough one so, we are not able to affirm that is not a V. cholerae O1 serotype. Vibrio cholerae Non-O1 strains, tested in Vero cells assay, produced cytotoxic effect within 24 h. It was found that 48/70 strains (66.6%), had cytotoxic activity, showing rounding and then lysis of cells. From our results we concluded that this cytotoxic effect, is not cholera toxin related, instead we propose it could be due to an unknown virulence factor, probably a different toxin in mexican Vibrio cholerae Non-O1 strains.

[Perspectives on cholera vaccines]

Perspectives of cholera vaccines with emphasis in their possible usage in Latin American countries are discussed. Microbiology, antigenicity, relevant aspects of traditional serology, protective immune responses and epidemiological data up to December, 1991, are presented. Indications of parenteral vaccines are discussed. Finally, perspectives of usage of cholera vaccines in Latin America are analyzed.

[Evaluation of the cold chain and follow-up of the potency of the antimeasles vaccine in the field]

In order to evaluate the quality of the measles vaccine, it was carried out a study in three states of Mexico (Durango, San Luis Potosi and Yucatan) during the intensive vaccination campaign in 1986. Edmonston-Zagreb measles vaccine vials were obtained from the different administrative-sanitary levels of the Ministry of Health in Mexico. Interviews were performed to the vaccine responsibles. Questionnaires had the following aspects of the cold chain: storage, preservation, control and transport of measles vaccine. Answers were evaluated through a system, where 100% indicated the necessary and sufficient level to get a good operating of the cold chain. The vaccine potency did not have variations under the minimum titre recommended for the World Health Organization (W.H.O.). The three states had the following compliment of the cold chain norms: 1) Central state level: 83% in storage, 80% in preservation, 100% in control and 100% in transport norms; 2) Regional level (jurisdiction): 87% in storage, 51% in preservation, 93% in control and 100% in transport norms; 3) Local level: 83% in storage, 64% in preservation, 83% in control and 33% in transport norms.

[Immuno-epidemiologic considerations on the prevention of measles in Mexico]

Study results of passive natural immunity anti-measles, and immune response to measles vaccine from different strains in Mexican children under one year old, are described in this paper. Mexican infants in these studies ended their maternal immunity at 8-10 months of age. Edmonston-Zagreb (EZ) vaccine strain had higher seroconversion rates comparing to Schwarz strain. Dose response effect was more closely related to Schwarz strain than EZ, since difference in seroconversion rates with standard, medium and high doses were statistically significant. However geometric mean post-vaccination titers were higher in children vaccinated with Schwarz strain, than EZ receptors.

[Lactation and weaning patterns in Mexico. 1986 National Health Survey]

In the process of nutrition, breastfeeding is fundamentally important, due to the nutritional and immunological value of the mother's milk. Within its beneficial effects, it is found that it improves weight and size in children. Another stage in the child's feeding that should be considered during the first year of life is the weaning that complements, at certain age of the breastfeeder, the nutrition given by breastmilk. The decrease or abandonment of breastfeeding is alarming in the developing countries, where this natural product is more available, economical and nutritious. There is evidence that within the health institutions, artificial feeding is encouraged. The National Health Survey collected basic information on sociodemographic variables risk factors, demand and use of health services. It also included questions on breastfeeding and weaning for the population under one year of age. It was found that 19.9 percent was never breastfed. Another important fact is that 42.4 percent of children received breastmilk for just three months or less. This view suggests that breastfeeding in our country is changing, due to various factors, among which we can mention the differences in life styles, education and economical development among states. The results of this study show interesting data that oblige us to consider more detailed and specific analyses in the future.

[Evaluation of the cold chain during the national antipoliomyelitis vaccination days. Mexico, 1987-1988]

An evaluation of the cold chain used during the "National Vaccination Days Against Poliomyelitis" in January and March of 1987 and 1988 was performed in 32 states of Mexico, both the potency of the trivalent Sabin vaccine and completion of requirements for the maintenance of the cold chain were evaluated at each level in the Ministry of Health's structure. Only 56 percent of the refrigeration units exclusively stored vaccines, more than 10 percent of refrigerators were broken, and 44 percent of the persons responsible for the cold chain system considered the storage capacity inadequate. A correlation was found between non-fulfillment of maintenance requirements for cold chain and a decreased in vaccine potency.

[Years of potential life lost: their usefulness in the analysis of mortality in Mexico]

The evolution of the epidemiology of mortality in developing countries requires the use of indicators additional to cause specific mortality rates. This paper presents the leading causes of potential years of life lost in Mexico in 1983, by sex. Methodologic discussion focused on age limits and relative numbers. The indicator proved useful to assess the impact of infectious diseases, accidents and homicides as causes of premature death. It was also useful to identify years of potential life lost attributable to specific age and sex groups. The use of years of potential life lost provides valuable information to epidemiologic mortality analysis.

[Seroconversion with trivalent Sabin vaccine in children less than four years of age]

A group of 58 children under 4 years old, were vaccinated with trivalent oral poliovirus vaccine Sabin (OPV), in two sanitary areas of Chiapas, Mexico. The complement of procedures for the maintenance of the cold chain, and the changes in the potency of the vaccine prior and after the vaccination were evaluated. Nurses got a blood sample of 3cc and other one, four weeks after vaccination in order to evaluate the seroconversion rate attributable to Sabin vaccine, which was analyzed through neutralization serologic test. Moreover the investigation team got a sample of feces one day prior to vaccination and other one every week in the following three weeks to vaccination date in order to isolate the poliovirus in the feces of the children. The high pre-vaccination seropositivity suggests that in these areas exist a wide circulation of poliovirus, which probably were vaccine viruses and in less proportion wild viruses. The seroconversion rates were low for the three types of poliovirus, nevertheless 83% of the children had at least one of the three possibilities of seroconversion: unique, double or triple. Children with pre-vaccine seropositive probably had a secondary immune response.