Since pertussis cases have been observed sporadically in Matsudo City, Chiba Prefecture, a clinical, bacteriological and serological study was carried out. The result obtained was as follows:
1) The serotype of the agent isolated was all classified as 1-3 type.
2) Typical clinical symptom of pertussis has been observed in a number of younger children and infants, however, atypical form has also been found in considerably high percentage.
3) The agglutinin titer against the newly isolated strains in the sera of both the patients and the healthy persons was higher than that against the standard strain (Maeno strain).
4) A trial using micro-titer technique for the agglutination was made and the titer was compaired with that of the classical tube method. The results from the both methods were well matched. The micro-titer technique was able to save definitely the quantity of sera and the manpower.
5) Adding gelatine and crystal violet to the dilution for agglutination test has advantage to make it easy to read the result and to avoid individual reading difference.
6) A comparison on the agglutinin titer of the school children in the prevarent and the non-prevalent area of the disease was made and found no significant difference between the areas.

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The antibody response to influenza neuraminidase was studied in serum following natural infections and immunizations with inactivated bivalent influenza A/Aichi/2/68 (H3 N2) and B/Kagoshima/1/68 virus vaccines. The neuraminidase-inhibition (NI) test was carried out by a modification of Laver-Kilbourne method using partially purified neuraminidase preparation.
The inactivated vaccines, both plain (200 CCA units per ml) and subunits vaccine (1200 CCA units per ml), were found to produce lower NI antibody as compared with HI antibody. In type A, only 5 of 55 (9 per cent) and in type B, 6 of 54 (11 per cent) of volunteers subcutaneously innoculated subunits vaccines showed a fourfold or greater rise in NI antibody titers. Duration of NI antibody possession after innoculation resembles to that of HI antibody.
The NI test seems to be a valuable method for serological diagnosis of influenza if prevalent virus strains are used. Increasing NI antibody titer were detected in 33 of 55 (60 per cent) sera of influenza A infections and in 30 of 42 (71 per cent) sera of influenza B infections, while with complement-fixation test, 58 per cent of type A to 79 per cent of type B, and with hemagglutination inhibition tests, 80 per cent of type A to 86 per cent of type B infections showed increasing titer. Duration of NI antibody possession after the infection is as long as that of HI antibody.
In some patients, born before 1930, increasing NI antibody titers against A/Swine/30 (Hsw 1 N 1) were seen, which demonstrates the doctrine of the so-called original antigenic sin.
NI antibodies prior to the onset of the illness were investigated at the time of influenza B epidemic in 1973 to study its protective effects against the infection. No significant difference was seen in the titers between serologically confirmed influenza patients and non-infected persons. So its protective effects are remained doubtful. However, among the infected cases, comparative studies showed that the higher NI antibody titers (≥1: 16) were seen among the afebrile cases than among the febrile cases. Further, the clinical statistics showed the high NI antibody is beneficial for the alleviation of the clinical symptoms.
These observations indicate the importance to examine the antibody response to the neuraminidase as well as hemagglutinin antigen in the serological diagnosis and the evaluation of influenza vaccines.

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