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NON-USEFULNESS OF MENINGOCOCCAL CARRIAGE-RATES
205 It is therefore clear that the level of circulating thyroid hormone does not influence T-lymphocyte dynamics, contrary to the suggestion of Aoki et al. N. R. FARID C. VON WESTARP V. V. Row R. VOLPE.
Endocrinology Research Laboratory,
Wellesley Hospital, Toronto, Ontario M4Y 1J3, Canada.
NON-USEFULNESS OF MENINGOCOCCAL CARRIAGE-RATES and others1 described meningococcal SIR,-Fraser in various carriage-rates populations of disparate age-groups in Great Britain. In their interesting discussion, the authors did not crystallise their thoughts on the usefulness of nasopharyngeal carriage-rate statistics. They correctly emphasised that high carriage-rates are often associated with no clinical disease, and vice versa. We wish to point out that, in terms of the dynamics of meningococcal infection, it is not the carriage-rate at all that has meaning; rather, instead, it is the acquisition-rate which is important -the number of new carriers over a short period of time. At Camp Lejeune, North Carolina, a Marine recruit training base, we noted high carriage-rates of meningococcal organisms in the summer of 1970 associated with no clinical disease and a decreasing rate of new acquisitions (see figure). In November, 1971, when clinical disease began there was the lowest overall carriage-rate observed, but the slope of the carriage-rate (the acquisition-rate) was rising sharply. Increasing cases of meningococcal disease due mostly to group-C organisms were noted in subsequent months. Throughout much of the study period the carriers had group-Y organisms, yet the cases were caused by group-C organisms. Epidemiologically, we knew that group-C organisms were virulent in terms of the propensity to cause most clinical disease. However, overall carriage-rates said nothing about new acquisitions; in fact, at many points in the study period it was group-Y organisms which were most prevalent. The importance of the acquisition-rate is also consistent with the observations of Goldschneider et al.,2 who showed in a prospective study that 38% of military recruits who acquired meningococcal Fraser, P. K., Bailey, G. K., Abbott, J. D., Gill, J. B., Walker, D. J. C. Lancet, 1973, i, 1235. 2. Goldschneider, I., Gotschlich, E. C., Artenstein, M. S. J. exp. Med. 1969, 129, 1327. 1.
MONTH
Carrier-rate and
OF
STUDY
1970 -71
Lejeune,
serogroup composition in trainees at North Carolina.
Hospital
cases
Camp
and respective serogroup composition are shown case in January and one of the clinical cases in February were in men within 6 months of trainee graduation, still remaining on base.
on
top.
The
single
organisms in their nasopharynx and subsequently developed clinical disease had no pre-existing bactericidal antibody to the epidemic strain. Epidemiologists would therefore desire to identify those susceptible hosts (without bactericidal antibody) who newly acquired a virulent meningococcal organism. With respect to virulence, there have been papers 3-5 which have shown that within meningococcal serogroups B or C there are a number of types, one of which (in each study) was found to be the major epidemic strain, and thus identified as virulent. In summary, the meningococcal carrier-rate, a statistic measure, says nothing about the dynamics of meningococcal infection, which can only be appreciated by knowing the
meningococcal acquisition-rate. Secondly, although mass culturing data may occasionally be helpful in an epidemic situation, they certainly fail to indicate within a serogroup whether or not a person is carrying a virulent organism. Of a large number of carriers of group-C organisms, only one or two may harbour the epidemic (virulent) strain and be at risk. For the same reasons, the knowledge of meningococcal carriage serogroup data from contacts of clinical cases may not clearly indicate who should or should not be on drug prophylaxis unless serotyping is performed to identify the virulent strain. Department of Medicine, University of Virginia School of Medicine,
Charlottesville, Virginia 22901, U.S.A. Virology Division, Naval Medical Field Research Laboratory,
Camp Lejeune, North Carolina 28542, U.S.A.
RICHARD P. WENZEL.
JOHN A. DAVIES JOHN R. MITZEL WALTER E. BEAM,
JR.
MEASUREMENT OF LUNG FUNCTION IN ASTHMA CLINIC
SiR,—The measurement of simple lung function at each attendance at the clinic has become an almost essential part of the management of patients with asthma. Conventional direct-writing spirometers of the wet or dry type are generally time-consuming, and a number of alternative versions of spirometer have been produced. We have recently investigated the Monaghan M-403 automatic spirometer in a children’s asthma outpatient clinic. The machine operates through a heated thermister and gives a direct digital read-out of the forced expired volume in one second (F.E,V’l)’ forced vital capacity (F.v.c.), and peak expiratory flow rate (P.E.F.), and it can also give values for peak inspiratory flow rate and the " sprint " maximum voluntary ventilation (M.V.V.). The Monaghan spirometer was connected in series with a conventional water spirometer (P. K. Morgan) and the F.E,V’l and F.v.c. were measured on 20 children. A high degree of correlation was found (r= 0-92 and 0-95, respectively). Similarly, comparisons were made of P.E.F. by connecting the Monaghan spirometer in series with a Wright peak flow meter and making measurements in 10 children. The correlation here was exceptionally good (r= 0-99). A further series of measurements were made using the Monaghan spirometer, wet spirometer, and peak flow meter consecutively and not connected in series. In this case the correlation between the two instruments was not as good as when the instruments were connected, and we believe this was due to subject variation. The " sprint " M.v.v. estimated by the Monaghan machine agreed with that measured by the wet spirometer, allowing Gold, R., Winklehake, J. L., Mars, R. S., Artenstein, J. infect. Dis. 1971, 124, 593. 4. Counts, G. W., Seeley, L., Beaty, H. N. ibid. p. 26. 5. Frasch, C. E., Chapman, S. S. ibid. 1973, 127, 149. 3.
M. S.
Endocrinology Research Laboratory,
Wellesley Hospital, Toronto, Ontario M4Y 1J3, Canada.
NON-USEFULNESS OF MENINGOCOCCAL CARRIAGE-RATES and others1 described meningococcal SIR,-Fraser in various carriage-rates populations of disparate age-groups in Great Britain. In their interesting discussion, the authors did not crystallise their thoughts on the usefulness of nasopharyngeal carriage-rate statistics. They correctly emphasised that high carriage-rates are often associated with no clinical disease, and vice versa. We wish to point out that, in terms of the dynamics of meningococcal infection, it is not the carriage-rate at all that has meaning; rather, instead, it is the acquisition-rate which is important -the number of new carriers over a short period of time. At Camp Lejeune, North Carolina, a Marine recruit training base, we noted high carriage-rates of meningococcal organisms in the summer of 1970 associated with no clinical disease and a decreasing rate of new acquisitions (see figure). In November, 1971, when clinical disease began there was the lowest overall carriage-rate observed, but the slope of the carriage-rate (the acquisition-rate) was rising sharply. Increasing cases of meningococcal disease due mostly to group-C organisms were noted in subsequent months. Throughout much of the study period the carriers had group-Y organisms, yet the cases were caused by group-C organisms. Epidemiologically, we knew that group-C organisms were virulent in terms of the propensity to cause most clinical disease. However, overall carriage-rates said nothing about new acquisitions; in fact, at many points in the study period it was group-Y organisms which were most prevalent. The importance of the acquisition-rate is also consistent with the observations of Goldschneider et al.,2 who showed in a prospective study that 38% of military recruits who acquired meningococcal Fraser, P. K., Bailey, G. K., Abbott, J. D., Gill, J. B., Walker, D. J. C. Lancet, 1973, i, 1235. 2. Goldschneider, I., Gotschlich, E. C., Artenstein, M. S. J. exp. Med. 1969, 129, 1327. 1.
MONTH
Carrier-rate and
OF
STUDY
1970 -71
Lejeune,
serogroup composition in trainees at North Carolina.
Hospital
cases
Camp
and respective serogroup composition are shown case in January and one of the clinical cases in February were in men within 6 months of trainee graduation, still remaining on base.
on
top.
The
single
organisms in their nasopharynx and subsequently developed clinical disease had no pre-existing bactericidal antibody to the epidemic strain. Epidemiologists would therefore desire to identify those susceptible hosts (without bactericidal antibody) who newly acquired a virulent meningococcal organism. With respect to virulence, there have been papers 3-5 which have shown that within meningococcal serogroups B or C there are a number of types, one of which (in each study) was found to be the major epidemic strain, and thus identified as virulent. In summary, the meningococcal carrier-rate, a statistic measure, says nothing about the dynamics of meningococcal infection, which can only be appreciated by knowing the
meningococcal acquisition-rate. Secondly, although mass culturing data may occasionally be helpful in an epidemic situation, they certainly fail to indicate within a serogroup whether or not a person is carrying a virulent organism. Of a large number of carriers of group-C organisms, only one or two may harbour the epidemic (virulent) strain and be at risk. For the same reasons, the knowledge of meningococcal carriage serogroup data from contacts of clinical cases may not clearly indicate who should or should not be on drug prophylaxis unless serotyping is performed to identify the virulent strain. Department of Medicine, University of Virginia School of Medicine,
Charlottesville, Virginia 22901, U.S.A. Virology Division, Naval Medical Field Research Laboratory,
Camp Lejeune, North Carolina 28542, U.S.A.
RICHARD P. WENZEL.
JOHN A. DAVIES JOHN R. MITZEL WALTER E. BEAM,
JR.
MEASUREMENT OF LUNG FUNCTION IN ASTHMA CLINIC
SiR,—The measurement of simple lung function at each attendance at the clinic has become an almost essential part of the management of patients with asthma. Conventional direct-writing spirometers of the wet or dry type are generally time-consuming, and a number of alternative versions of spirometer have been produced. We have recently investigated the Monaghan M-403 automatic spirometer in a children’s asthma outpatient clinic. The machine operates through a heated thermister and gives a direct digital read-out of the forced expired volume in one second (F.E,V’l)’ forced vital capacity (F.v.c.), and peak expiratory flow rate (P.E.F.), and it can also give values for peak inspiratory flow rate and the " sprint " maximum voluntary ventilation (M.V.V.). The Monaghan spirometer was connected in series with a conventional water spirometer (P. K. Morgan) and the F.E,V’l and F.v.c. were measured on 20 children. A high degree of correlation was found (r= 0-92 and 0-95, respectively). Similarly, comparisons were made of P.E.F. by connecting the Monaghan spirometer in series with a Wright peak flow meter and making measurements in 10 children. The correlation here was exceptionally good (r= 0-99). A further series of measurements were made using the Monaghan spirometer, wet spirometer, and peak flow meter consecutively and not connected in series. In this case the correlation between the two instruments was not as good as when the instruments were connected, and we believe this was due to subject variation. The " sprint " M.v.v. estimated by the Monaghan machine agreed with that measured by the wet spirometer, allowing Gold, R., Winklehake, J. L., Mars, R. S., Artenstein, J. infect. Dis. 1971, 124, 593. 4. Counts, G. W., Seeley, L., Beaty, H. N. ibid. p. 26. 5. Frasch, C. E., Chapman, S. S. ibid. 1973, 127, 149. 3.
M. S.